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37      <p>
38            An important part of DB's transactional guarantees is durability.
39            <span class="emphasis"><em>Durability</em></span> means that once a
40            transaction has been committed, the database modifications performed
41            under its protection will not be lost due to system failure.
42        </p>
43      <p>
44            In order to provide the transactional durability guarantee, 
45            DB uses a write-ahead logging system. Every operation performed on
46            your databases is described in a log before it is performed on
47            your databases. This is done in order to ensure that an operation can be
48            recovered in the event of an untimely application 
49            or system failure. 
50        </p>
51      <p>
52            <span>
53            Beyond logging, another important aspect of durability is
54            recoverability. That is,  backup and restore. </span> 
55            
56            DB supports a normal recovery that runs against a subset of
57            your log files. This is a routine procedure used whenever your
58            environment is first opened upon application startup, and it is intended to
59            ensure that your database is in a consistent state.  DB also
60            supports archival backup and recovery in the case of
61            catastrophic failure, such as the loss of a physical disk
62            drive.
63        </p>
64      <p>
65            This book describes several different backup procedures
66            you can use to protect your on-disk data. These procedures
67            range from simple offline backup strategies to hot failovers. Hot failovers
68            provide not only a backup mechanism, but
69            also a way to recover from a fatal hardware failure.
70        </p>
71      <p>
72            This book also describes the recovery procedures you should use
73            for each of the backup strategies that you might employ.
74        </p>
75      <p>
76            For a detailed description of backup and restore procedures, see
77            <span> 
78                <a href="filemanagement.html">Managing DB Files</a>.
79            </span>
80            
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