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<th colspan="3" align="center">Replication Manager methods</th>
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<th width="60%" align="center">Chapter 12.
Berkeley DB Replication
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<h2 class="title" style="clear: both"><a id="rep_mgr_meth"></a>Replication Manager methods</h2>
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<p>
Applications which use the Replication Manager support generally
call the following Berkeley DB methods. The general pattern is to
call various methods to configure Replication Manager, and then
start it by calling <a href="../api_reference/C/repmgrstart.html" class="olink">DB_ENV->repmgr_start()</a>. Once this initialization is
complete, the application rarely needs to call any of these
methods. (A prime example of an exception to this rule would be
the <a href="../api_reference/C/repsync.html" class="olink">DB_ENV->rep_sync()</a> method, if the application is
<a class="xref" href="rep_mastersync.html#rep_delay_sync" title="Delaying client synchronization">Delaying client synchronization</a>.)
</p>
<div class="variablelist">
<dl>
<dt>
<span class="term">
<a href="../api_reference/C/db_site.html" class="olink">DB_SITE</a>
</span>
</dt>
<dd>
<p>
The <a href="../api_reference/C/db_site.html" class="olink">DB_SITE</a> handle is used to configure a site that
belongs to the replication group. You can obtain a <a href="../api_reference/C/db_site.html" class="olink">DB_SITE</a>
handle by calling the <a href="../api_reference/C/repmgr_site.html" class="olink">DB_ENV->repmgr_site()</a> method. When you do this, you
provide the TCP/IP host name and port that the replication
site uses for incoming connections.
</p>
<p>
Once you have the <a href="../api_reference/C/db_site.html" class="olink">DB_SITE</a> handle, you use the
<a href="../api_reference/C/dbsite_set_config.html" class="olink">DB_SITE->set_config()</a> method to configure the handle. One of
the things you can configure about the handle is whether it
is the local site (using the <code class="literal">DB_LOCAL_SITE</code>
parameter). You must configure one and only one <a href="../api_reference/C/db_site.html" class="olink">DB_SITE</a> handle
to be a local site before you start replication.
</p>
<p>
You can also optionally configure <a href="../api_reference/C/db_site.html" class="olink">DB_SITE</a> handles for
remote sites to help Replication Manager startup more
efficiently. Note that it is usually not necessary for
each site in the replication group initially to know about
all other sites in the group. Sites can discover each
other dynamically, as described in
<a class="xref" href="rep_newsite.html" title="Connecting to a new site">Connecting to a new site</a>.
</p>
<p>
Once you have configured your <a href="../api_reference/C/db_site.html" class="olink">DB_SITE</a> handles, you start
replication using <a href="../api_reference/C/repmgrstart.html" class="olink">DB_ENV->repmgr_start()</a>.
</p>
<p>
When you are shutting down your application, you must
use the <a href="../api_reference/C/dbsite_close.html" class="olink">DB_SITE->close()</a> method to close
all your open <a href="../api_reference/C/db_site.html" class="olink">DB_SITE</a> handles before you close your
environment handles.
</p>
</dd>
<dt>
<span class="term">
<a href="../api_reference/C/repmgrset_ack_policy.html" class="olink">DB_ENV->repmgr_set_ack_policy()</a>
</span>
</dt>
<dd>
<p>
The <a href="../api_reference/C/repmgrset_ack_policy.html" class="olink">DB_ENV->repmgr_set_ack_policy()</a> method configures the acknowledgement
policy to be used in the replication group, in other words, the
behavior of the master with respect to acknowledgements for
"permanent" messages, which implements the application's
requirements for <a class="xref" href="rep_trans.html" title="Transactional guarantees">Transactional guarantees</a>. The current implementation
requires all sites in the replication group to configure the same
acknowledgement policy.
</p>
</dd>
<dt>
<span class="term">
<a href="../api_reference/C/reppriority.html" class="olink">DB_ENV->rep_set_priority()</a>
</span>
</dt>
<dd>
<p>
The <a href="../api_reference/C/reppriority.html" class="olink">DB_ENV->rep_set_priority()</a> method configures the local site's priority
for the purpose of elections.
</p>
</dd>
<dt>
<span class="term">
<a href="../api_reference/C/repset_timeout.html" class="olink">DB_ENV->rep_set_timeout()</a>
</span>
</dt>
<dd>
<p>
This method optionally configures various timeout values.
Otherwise default timeout values as specified in <a href="../api_reference/C/repset_timeout.html" class="olink">DB_ENV->rep_set_timeout()</a>
are used. In particular, Replication Manager client sites can
be configured to monitor the health of the TCP/IP connection to
the master site using heartbeat messages. If the client
receives no messages from the master for a certain amount of
time, it considers the connection to be broken, and calls for
an election to choose a new master. Heartbeat messages
also help clients request missing master changes in the
absence of master activity.
</p>
</dd>
<dt>
<span class="term">
<a href="../api_reference/C/envevent_notify.html" class="olink">DB_ENV->set_event_notify()</a>
</span>
</dt>
<dd>
<p>
Once configured and started, Replication Manager does virtually
all of its work in the background, usually without the need for
any direct communication with the application. However,
occasionally events occur which the application may be
interested in knowing about. The application can request
notification of these events by calling the <a href="../api_reference/C/envevent_notify.html" class="olink">DB_ENV->set_event_notify()</a>
method.
</p>
</dd>
<dt>
<span class="term">
<a href="../api_reference/C/repmgrstart.html" class="olink">DB_ENV->repmgr_start()</a>
</span>
</dt>
<dd>
<p>
The <a href="../api_reference/C/repmgrstart.html" class="olink">DB_ENV->repmgr_start()</a> method starts the replication system. It
opens the listening TCP/IP socket and creates all the
background processing threads that will be needed.
</p>
</dd>
</dl>
</div>
<p>
In addition to the methods previously described, Replication Manager
applications may also call the following methods, as needed:
<a href="../api_reference/C/repconfig.html" class="olink">DB_ENV->rep_set_config()</a>, <a href="../api_reference/C/repset_limit.html" class="olink">DB_ENV->rep_set_limit()</a>, <a href="../api_reference/C/repset_request.html" class="olink">DB_ENV->rep_set_request()</a>, <a href="../api_reference/C/repsync.html" class="olink">DB_ENV->rep_sync()</a> and <a href="../api_reference/C/repstat.html" class="olink">DB_ENV->rep_stat()</a>.
</p>
<p>
Finally, Replication Manager applications can also make use of the
Replication Manager's message channels. This allows the various
sites in the replication group to pass messages that are tailored
to the application's requirements. For more information, see
<a class="xref" href="repmgr_channels.html" title="Using Replication Manager message channels">Using Replication Manager message channels</a>.
</p>
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