Sindbad~EG File Manager
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<p>Library Version 18.1.40</p>
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<h2 class="title" style="clear: both"><a id="transapp_hotfail"></a>Hot failover</h2>
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<p>
For some applications, it may be useful to periodically
snapshot the database environment for use as a hot failover
should the primary system fail. The following steps can be
taken to keep a backup environment in close synchrony with an
active environment. The active environment is entirely
unaffected by these procedures, and both read and write
operations are allowed during all steps described here.
</p>
<p>
The procedure described here is not compatible with the
concurrent use of the transactional bulk insert optimization
(transactions started with the <a href="../api_reference/C/txnbegin.html#txnbegin_DB_TXN_BULK" class="olink">DB_TXN_BULK</a> flag). After the
bulk optimization is used, the archive must be created again
from scratch starting with step 1.
</p>
<p>
The <a href="../api_reference/C/db_hotbackup.html" class="olink">db_hotbackup</a> utility is the preferred way to automate
generating a hot failover system. The first step is to run
<a href="../api_reference/C/db_hotbackup.html" class="olink">db_hotbackup</a> utility without the <span class="bold"><strong>-u</strong></span>
flag. This will create hot backup copy of the databases in
your environment. After that point periodically running the
<a href="../api_reference/C/db_hotbackup.html" class="olink">db_hotbackup</a> utility with the <span class="bold"><strong>-u</strong></span>
flag will copy the new log files and run recovery on the
backup copy to bring it current with the primary environment.
</p>
<p>
Note that you can also create your own hot backup solution
using the <a href="../api_reference/C/envbackup.html" class="olink">DB_ENV->backup()</a> or <a href="../api_reference/C/envdbbackup.html" class="olink">DB_ENV->dbbackup()</a> methods.
</p>
<p>
To implement your own hot fail over system, the steps below
can be followed. However, care should be taken on non-UNIX
based systems when copying the database files to be sure that
they are either quiescent, or that either the <a href="../api_reference/C/envbackup.html" class="olink">DB_ENV->backup()</a> or
<a href="../api_reference/C/db_copy.html" class="olink">db_copy()</a> routine is used to ensure atomic reads of the
database pages.
</p>
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<ol type="1">
<li>
<p>
Run the <a href="../api_reference/C/db_archive.html" class="olink">db_archive</a> utility with the <span class="bold"><strong>-s</strong></span>
option in the active environment to
identify all of the active environment's database
files, and copy them to the backup directory.
</p>
<p>
If the database files are stored in a separate
directory from the other Berkeley DB files, it will be
simpler (and much faster!) to copy the directory
itself instead of the individual files (see
<a href="../api_reference/C/envadd_data_dir.html" class="olink">DB_ENV->add_data_dir()</a> for additional information).
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
If any of the database files did not have an
open <a href="../api_reference/C/db.html" class="olink">DB</a> handle during the lifetime of the
current log files, the <a href="../api_reference/C/db_archive.html" class="olink">db_archive</a> utility will not list
them in its output. This is another reason it may
be simpler to use a separate database file
directory and copy the entire directory instead of
archiving only the files listed by the
<a href="../api_reference/C/db_archive.html" class="olink">db_archive</a> utility.
</p>
</div>
</li>
<li>
Remove all existing log files from the backup
directory.
</li>
<li>
Run the <a href="../api_reference/C/db_archive.html" class="olink">db_archive</a> utility with the <span class="bold"><strong>-l</strong></span>
option in the active environment to
identify all of the active environment's log files, and
copy them to the backup directory.
</li>
<li>
Run the <a href="../api_reference/C/db_recover.html" class="olink">db_recover</a> utility with the <span class="bold"><strong>-c</strong></span> option
in the backup directory to catastrophically recover the copied environment.
</li>
</ol>
</div>
<p>
Steps 2, 3 and 4 may be repeated as often as you like. If
Step 1 (the initial copy of the database files) is repeated,
then Steps 2, 3 and 4 <span class="bold"><strong>must</strong></span> be
performed at least once in order to ensure a consistent
database environment snapshot.
</p>
<p>
These procedures must be integrated with your other
archival procedures, of course. If you are periodically
removing log files from your active environment, you must be
sure to copy them to the backup directory before removing them
from the active directory. Not copying a log file to the
backup directory and subsequently running recovery with it
present may leave the backup snapshot of the environment
corrupted. A simple way to ensure this never happens is to
archive the log files in Step 2 as you remove them from the
backup directory, and move inactive log files from your active
environment into your backup directory (rather than copying
them), in Step 3. The following steps describe this procedure
in more detail:
</p>
<div class="orderedlist">
<ol type="1">
<li>
Run the <a href="../api_reference/C/db_archive.html" class="olink">db_archive</a> utility with the <span class="bold"><strong>-s</strong></span> option
in the active environment to identify all of the active environment's database files,
and copy them to the backup directory.
</li>
<li>
Archive all existing log files from the backup
directory, moving them to a backup device such as CD-ROM,
alternate disk, or tape.
</li>
<li>
Run the <a href="../api_reference/C/db_archive.html" class="olink">db_archive</a> utility (without any option) in the
active environment to identify all of the log files in the
active environment that are no longer in use, and
<span class="bold"><strong>move</strong></span> them to the
backup directory.
</li>
<li>
Run the <a href="../api_reference/C/db_archive.html" class="olink">db_archive</a> utility with the <span class="bold"><strong>-l</strong></span> option
in the active environment to
identify all of the remaining log files in the active
environment, and <span class="bold"><strong>copy</strong></span> the
log files to the backup directory.
</li>
<li>
Run the <a href="../api_reference/C/db_recover.html" class="olink">db_recover</a> utility with the <span class="bold"><strong>-c</strong></span> option
in the backup directory to
catastrophically recover the copied environment.
</li>
</ol>
</div>
<p>
As before, steps 2, 3, 4 and 5 may be repeated as often as
you like. If Step 1 (the initial copy of the database files)
is repeated, then Steps 2 through 5 <span class="bold"><strong>must</strong></span> be
performed at least once in order to
ensure a consistent database environment snapshot.
</p>
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