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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Logging Subsystem</dl></h3></td>
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<h1 align=center>Berkeley DB and logging</h1>
<p>The logging subsystem is the logging facility used by Berkeley DB. It is
largely Berkeley DB specific, although it is potentially useful outside of
the Berkeley DB package for applications wanting write-ahead logging support.
Applications wanting to use the log for purposes other than logging file
modifications based on a set of open file descriptors will almost
certainly need to make source code modifications to the Berkeley DB code
base.
<p>A log can be shared by any number of threads of control. The
<a href="../../api_c/env_open.html">DBENV->open</a> interface is used to open a log. When the log is no
longer in use, it should be closed, using the <a href="../../api_c/env_close.html">DBENV->close</a>
interface.
<p>Individual log entries are identified by log sequence numbers. Log
sequence numbers are stored in an opaque object, a <a href="../../api_c/db_lsn.html">DB_LSN</a>.
<p>The <a href="../../api_c/log_put.html">log_put</a> interface is used to append new log records to the
log. Optionally, the <a href="../../api_c/log_put.html#DB_CHECKPOINT">DB_CHECKPOINT</a> flag can be used to output
a checkpoint log record (indicating that the log is consistent to that
point and recoverable after a system or application failure), as well
as open-file information. The <a href="../../api_c/log_get.html">log_get</a> interface is used to
retrieve log records from the log.
<p>There are additional interfaces for integrating the log subsystem with a
transaction processing system:
<p><dl compact>
<p><dt><a href="../../api_c/log_register.html">log_register</a> and <a href="../../api_c/log_unregister.html">log_unregister</a><dd>These interfaces associate files with identification numbers. These
identification numbers are logged so that transactional recovery
correctly associates log records with the appropriate files.
<p><dt><a href="../../api_c/log_flush.html">log_flush</a><dd>Flushes the log up to a particular log sequence number.
<p><dt><a href="../../api_c/log_compare.html">log_compare</a><dd>Allows applications to compare any two log sequence numbers.
<p><dt><a href="../../api_c/log_file.html">log_file</a> <dd>Maps a log sequence number to the specific log file which contains it.
<p><dt><a href="../../api_c/log_archive.html">log_archive</a><dd>Returns various sets of log file names. These interfaces are used for
database administration, e.g., to determine if log files may safely be
removed from the system.
<p><dt><a href="../../api_c/log_stat.html">log_stat</a> <dd>The display <a href="../../utility/db_stat.html">db_stat</a> utility uses the <a href="../../api_c/log_stat.html">log_stat</a> interface
to display statistics about the log.
<p><dt><a href="../../api_c/env_remove.html">DBENV->remove</a><dd>The log meta-information (but not the log files themselves) may be
removed using the <a href="../../api_c/env_remove.html">DBENV->remove</a> interface.
</dl>
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