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��16.�� The Logging Subsystem</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="Berkeley DB Programmer's Reference Guide" /> 10 <link rel="up" href="index.html" title="Berkeley DB Programmer's Reference Guide" /> 11 <link rel="prev" href="lock_nondb.html" title="Locking and non-Berkeley DB applications" /> 12 <link rel="next" href="log_config.html" title="Configuring logging" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Chapter��16.�� 19 The Logging Subsystem 20 </th> 21 </tr> 22 <tr> 23 <td width="20%" align="left"><a accesskey="p" href="lock_nondb.html">Prev</a>��</td> 24 <th width="60%" align="center">��</th> 25 <td width="20%" align="right">��<a accesskey="n" href="log_config.html">Next</a></td> 26 </tr> 27 </table> 28 <hr /> 29 </div> 30 <div class="chapter" lang="en" xml:lang="en"> 31 <div class="titlepage"> 32 <div> 33 <div> 34 <h2 class="title"><a id="log"></a>Chapter��16.�� 35 The Logging Subsystem 36 </h2> 37 </div> 38 </div> 39 </div> 40 <div class="toc"> 41 <p> 42 <b>Table of Contents</b> 43 </p> 44 <dl> 45 <dt> 46 <span class="sect1"> 47 <a href="log.html#log_intro">Introduction to the logging subsystem</a> 48 </span> 49 </dt> 50 <dt> 51 <span class="sect1"> 52 <a href="log_config.html">Configuring logging</a> 53 </span> 54 </dt> 55 <dt> 56 <span class="sect1"> 57 <a href="log_limits.html">Log file limits</a> 58 </span> 59 </dt> 60 </dl> 61 </div> 62 <div class="sect1" lang="en" xml:lang="en"> 63 <div class="titlepage"> 64 <div> 65 <div> 66 <h2 class="title" style="clear: both"><a id="log_intro"></a>Introduction to the logging subsystem</h2> 67 </div> 68 </div> 69 </div> 70 <p>The Logging subsystem is the logging facility used by Berkeley DB. It is 71largely Berkeley DB-specific, although it is potentially useful outside of 72the Berkeley DB package for applications wanting write-ahead logging support. 73Applications wanting to use the log for purposes other than logging file 74modifications based on a set of open file descriptors will almost 75certainly need to make source code modifications to the Berkeley DB code 76base.</p> 77 <p>A log can be shared by any number of threads of control. The 78<a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a> method is used to open a log. When the log is no longer 79in use, it should be closed using the <a href="../api_reference/C/envclose.html" class="olink">DB_ENV->close()</a> method.</p> 80 <p>Individual log entries are identified by log sequence numbers. Log 81sequence numbers are stored in an opaque object, an <a href="../api_reference/C/lsn.html" class="olink">DB_LSN</a>.</p> 82 <p>The <a href="../api_reference/C/logcursor.html" class="olink">DB_ENV->log_cursor()</a> method is used to allocate a log cursor. Log cursors 83have two methods: <a href="../api_reference/C/logcget.html" class="olink">DB_LOGC->get()</a> method to retrieve log records from the 84log, and <a href="../api_reference/C/logcclose.html" class="olink">DB_LOGC->close()</a> method to destroy the cursor.</p> 85 <p>There are additional methods for integrating the log subsystem with a 86transaction processing system:</p> 87 <div class="variablelist"> 88 <dl> 89 <dt> 90 <span class="term"> 91 <a href="../api_reference/C/logflush.html" class="olink">DB_ENV->log_flush()</a> 92 </span> 93 </dt> 94 <dd>Flushes the log up to a particular log sequence number.</dd> 95 <dt> 96 <span class="term"> 97 <a href="../api_reference/C/logcompare.html" class="olink">DB_ENV->log_compare()</a> 98 </span> 99 </dt> 100 <dd>Allows applications to compare any two log sequence numbers.</dd> 101 <dt> 102 <span class="term"> 103 <a href="../api_reference/C/logfile.html" class="olink">DB_ENV->log_file()</a> 104 </span> 105 </dt> 106 <dd>Maps a log sequence number to the specific log file that contains it.</dd> 107 <dt> 108 <span class="term"> 109 <a href="../api_reference/C/logarchive.html" class="olink">DB_ENV->log_archive()</a> 110 </span> 111 </dt> 112 <dd>Returns various sets of log filenames. These methods are used for 113database administration; for example, to determine if log files may 114safely be removed from the system.</dd> 115 <dt> 116 <span class="term"> 117 <a href="../api_reference/C/logstat.html" class="olink">DB_ENV->log_stat()</a> 118 </span> 119 </dt> 120 <dd> The display <a href="../api_reference/C/db_stat.html" class="olink">db_stat utility</a> utility used the <a href="../api_reference/C/logstat.html" class="olink">DB_ENV->log_stat()</a> method to 121display statistics about the log.</dd> 122 <dt> 123 <span class="term"> 124 <a href="../api_reference/C/envremove.html" class="olink">DB_ENV->remove()</a> 125 </span> 126 </dt> 127 <dd>The log meta-information (but not the log files themselves) may be 128removed using the <a href="../api_reference/C/envremove.html" class="olink">DB_ENV->remove()</a> method.</dd> 129 </dl> 130 </div> 131 <div class="informaltable"> 132 <table border="1" width="80%"> 133 <colgroup> 134 <col /> 135 <col /> 136 </colgroup> 137 <thead> 138 <tr> 139 <th>Logging Subsystem and Related Methods</th> 140 <th>Description</th> 141 </tr> 142 </thead> 143 <tbody> 144 <tr> 145 <td> 146 <a href="../api_reference/C/lsn.html" class="olink">DB_LSN</a> 147 </td> 148 <td>Log Sequence Numbers</td> 149 </tr> 150 <tr> 151 <td> 152 <a href="../api_reference/C/logcompare.html" class="olink">DB_ENV->log_compare()</a> 153 </td> 154 <td>Compare two Log Sequence Numbers</td> 155 </tr> 156 <tr> 157 <td> 158 <a href="../api_reference/C/logarchive.html" class="olink">DB_ENV->log_archive()</a> 159 </td> 160 <td>List log and database files</td> 161 </tr> 162 <tr> 163 <td> 164 <a href="../api_reference/C/logfile.html" class="olink">DB_ENV->log_file()</a> 165 </td> 166 <td>Map Log Sequence Numbers to log files</td> 167 </tr> 168 <tr> 169 <td> 170 <a href="../api_reference/C/logflush.html" class="olink">DB_ENV->log_flush()</a> 171 </td> 172 <td>Flush log records</td> 173 </tr> 174 <tr> 175 <td> 176 <a href="../api_reference/C/logprintf.html" class="olink">DB_ENV->log_printf()</a> 177 </td> 178 <td>Append informational message to the log</td> 179 </tr> 180 <tr> 181 <td> 182 <a href="../api_reference/C/logput.html" class="olink">DB_ENV->log_put()</a> 183 </td> 184 <td>Write a log record</td> 185 </tr> 186 <tr> 187 <td> 188 <a href="../api_reference/C/logstat.html" class="olink">DB_ENV->log_stat()</a> 189 </td> 190 <td>Return log subsystem statistics</td> 191 </tr> 192 <tr> 193 <td> 194 <span class="emphasis"> 195 <em>Logging Subsystem Cursors</em> 196 </span> 197 </td> 198 <td>��</td> 199 </tr> 200 <tr> 201 <td> 202 <a href="../api_reference/C/logcursor.html" class="olink">DB_ENV->log_cursor()</a> 203 </td> 204 <td>Create a log cursor handle</td> 205 </tr> 206 <tr> 207 <td> 208 <a href="../api_reference/C/logcclose.html" class="olink">DB_LOGC->close()</a> 209 </td> 210 <td>Close a log cursor</td> 211 </tr> 212 <tr> 213 <td> 214 <a href="../api_reference/C/logcget.html" class="olink">DB_LOGC->get()</a> 215 </td> 216 <td>Retrieve a log record</td> 217 </tr> 218 <tr> 219 <td> 220 <span class="emphasis"> 221 <em>Logging Subsystem Configuration</em> 222 </span> 223 </td> 224 <td>��</td> 225 </tr> 226 <tr> 227 <td> 228 <a href="../api_reference/C/envlog_set_config.html" class="olink">DB_ENV->log_set_config()</a> 229 </td> 230 <td>Configure the logging subsystem</td> 231 </tr> 232 <tr> 233 <td> 234 <a href="../api_reference/C/envset_lg_bsize.html" class="olink">DB_ENV->set_lg_bsize()</a> 235 </td> 236 <td>Set log buffer size</td> 237 </tr> 238 <tr> 239 <td> 240 <a href="../api_reference/C/envset_lg_dir.html" class="olink">DB_ENV->set_lg_dir()</a> 241 </td> 242 <td>Set the environment logging directory</td> 243 </tr> 244 <tr> 245 <td> 246 <a href="../api_reference/C/envset_lg_filemode.html" class="olink">DB_ENV->set_lg_filemode()</a> 247 </td> 248 <td>Set log file mode</td> 249 </tr> 250 <tr> 251 <td> 252 <a href="../api_reference/C/envset_lg_max.html" class="olink">DB_ENV->set_lg_max()</a> 253 </td> 254 <td>Set log file size</td> 255 </tr> 256 <tr> 257 <td> 258 <a href="../api_reference/C/envset_lg_regionmax.html" class="olink">DB_ENV->set_lg_regionmax()</a> 259 </td> 260 <td>Set logging region size</td> 261 </tr> 262 </tbody> 263 </table> 264 </div> 265 </div> 266 </div> 267 <div class="navfooter"> 268 <hr /> 269 <table width="100%" summary="Navigation footer"> 270 <tr> 271 <td width="40%" align="left"><a accesskey="p" href="lock_nondb.html">Prev</a>��</td> 272 <td width="20%" align="center">��</td> 273 <td width="40%" align="right">��<a accesskey="n" href="log_config.html">Next</a></td> 274 </tr> 275 <tr> 276 <td width="40%" align="left" valign="top">Locking and non-Berkeley DB applications��</td> 277 <td width="20%" align="center"> 278 <a accesskey="h" href="index.html">Home</a> 279 </td> 280 <td width="40%" align="right" valign="top">��Configuring logging</td> 281 </tr> 282 </table> 283 </div> 284 </body> 285</html> 286