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<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
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<div>
<h2 class="title" style="clear: both"><a id="recovery"></a>Recovery Procedures</h2>
</div>
</div>
<div></div>
</div>
<p>
DB supports two types of recovery:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
Normal recovery, which is run when your environment is
opened upon application startup, examines only those
log records needed to bring the databases to a consistent
state since the last checkpoint. Normal recovery
starts with any logs used by any transactions active at
the time of the last checkpoint, and examines all logs
from then to the current logs.
</p>
</li>
<li>
<p>
Catastrophic recovery, which is performed in the same
way that normal recovery is except that it examines
all available log files. You use catastrophic recovery
to restore your databases from a previously created backup.
</p>
</li>
</ul>
</div>
<p>
Of these two, normal recovery should be considered a routine
matter; in fact you should run normal
recovery whenever you start up your application.
</p>
<p>
Catastrophic recovery is run whenever you have lost or
corrupted your database files and you want to restore from a
backup. You also run catastrophic recovery when
you create a hot backup
(see <a href="hotfailover.html">Using Hot Failovers</a> for more information).
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="normalrecovery"></a>Normal Recovery</h3>
</div>
</div>
<div></div>
</div>
<p>
Normal recovery examines the contents of your environment's
log files, and uses this information to ensure that your
database files are consistent relative to the
information contained in the log files.
</p>
<p>
Normal recovery also recreates your environment's region files.
This has the desired effect of clearing any unreleased locks
that your application may have held at the time of an
unclean application shutdown.
</p>
<p>
Normal recovery is run only against those log files created
since the time of your last checkpoint. For this reason,
your recovery time is dependent on how much data has been
written since the last checkpoint, and therefore on how
much log file information there is to examine. If you run
checkpoints infrequently, then normal recovery can
take a relatively long time.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
You should run normal recovery every
time you perform application startup.
</p>
</div>
<p>
To run normal recovery:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
Make sure all your environment handles are closed.
</p>
</li>
<li>
<p>
Normal recovery <span class="emphasis"><em>must
be</em></span> single-threaded.
</p>
</li>
<li>
<p>
Provide the <tt class="literal">DB_RECOVER</tt> flag when
you open your environment.
</p>
</li>
</ul>
</div>
<p>
You can also run recovery by pausing or shutting down your
application and using the <span><b class="command">db_recover</b></span>
command line utility.
</p>
<p>
For example:
</p>
<pre class="programlisting">#include "db_cxx.h"
...
void *checkpoint_thread(void *);
int main(void)
{
u_int32_t env_flags = DB_CREATE | // If the environment does not
// exist, create it.
DB_INIT_LOCK | // Initialize locking
DB_INIT_LOG | // Initialize logging
DB_INIT_MPOOL | // Initialize the cache
DB_INIT_TXN | // Initialize transactions
DB_THREAD | // Free-thread the env handle
DB_RECOVER; // Run normal recovery
std::string envHome("/export1/testEnv");
DbEnv myEnv(0);
try {
myEnv.open(envHome.c_str(), env_flags, 0);
...
// All other operations are identical from here. Notice, however,
// that we have not created any other threads of control before
// recovery is complete. You want to run recovery for
// the first thread in your application that opens an environment,
// but not for any subsequent threads. </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="catastrophicrecovery"></a>Catastrophic Recovery</h3>
</div>
</div>
<div></div>
</div>
<p>
Use catastrophic recovery when you are
recovering your databases from a previously created backup.
Note that to restore your databases from a previous backup, you
should copy the backup to a new environment directory, and
then run catastrophic recovery. Failure to do so can lead to
the internal database structures being out of sync with your log files.
</p>
<p>
Catastrophic recovery must be run single-threaded.
</p>
<p>
To run catastrophic recovery:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
Shutdown all database operations.
</p>
</li>
<li>
<p>
Restore the backup to an empty directory.
</p>
</li>
<li>
<p>
Provide the <tt class="literal">DB_RECOVER_FATAL</tt> flag when
you open your environment. This environment open
must be single-threaded.
</p>
</li>
</ul>
</div>
<p>
You can also run recovery by pausing or shutting down your
application and using the <span><b class="command">db_recover</b></span>
command line utility with the the <tt class="literal">-c</tt> option.
</p>
<p>
Note that catastrophic recovery examines every available
log file — not just those log files created since the
last checkpoint as is the case for normal recovery. For this reason,
catastrophic recovery is likely to take longer than does
normal recovery.
</p>
<p>
For example:
</p>
<pre class="programlisting">#include "db_cxx.h"
...
void *checkpoint_thread(void *);
int main(void)
{
u_int32_t env_flags = DB_CREATE | // If the environment does not
// exist, create it.
DB_INIT_LOCK | // Initialize locking
DB_INIT_LOG | // Initialize logging
DB_INIT_MPOOL | // Initialize the cache
DB_INIT_TXN | // Initialize transactions
DB_THREAD | // Free-thread the env handle
<b class="userinput"><tt>DB_RECOVER_FATAL; // Run catastrophic recovery</tt></b>
std::string envHome("/export1/testEnv");
DbEnv myEnv(0);
try {
myEnv.open(envHome.c_str(), env_flags, 0);
...
// All other operations are identical from here. Notice, however,
// that we have not created any other threads of control before
// recovery is complete. You want to run recovery for
// the first thread in your application that opens an environment,
// but not for any subsequent threads. </pre>
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