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<div>
<h2 class="title" style="clear: both"><a id="rep_ex"></a>Ex_rep: a replication example</h2>
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<p>Ex_rep, found in the <code class="filename">examples_c/ex_rep</code> subdirectory
of the Berkeley DB distribution, is a simple but complete demonstration of a
replicated application. The application is a mock stock ticker. The
master accepts a stock symbol and a numerical value as input, and
stores this information into a replicated database; either master or
clients can display the contents of the database, given an empty input
line.</p>
<p>There are two versions of the application: ex_rep_mgr uses Replication
Manager, while ex_rep_base uses the replication Base API. This is
intended to demonstrate that, while the basic function of the
application is the same in either case, the replication support
infrastructure differs markedly.</p>
<p>The communication infrastructure demonstrated with ex_rep_base has the
same dependencies on system networking and threading support as does
the Replication Manager (see the <a class="xref" href="rep.html#rep_intro" title="Replication introduction">Replication introduction</a>). The Makefile created by the standard UNIX
configuration will build the ex_rep examples on most platforms. Enter
"make ex_rep_mgr" and/or "make ex_rep_base" to build them.</p>
<p>The synopsis for both programs is as follows:</p>
<code class="literal">ex_rep_xxx <span class="bold"><strong>-h home</strong></span> <span class="bold"><strong>-l host:port</strong></span> [<span class="bold"><strong>-MC</strong></span>] [<span class="bold"><strong>-r host:port</strong></span>] [<span class="bold"><strong>-R host:port</strong></span>] [<span class="bold"><strong>-a all|quorum</strong></span>] [<span class="bold"><strong>-b</strong></span>] [<span class="bold"><strong>-n sites</strong></span>] [<span class="bold"><strong>-p priority</strong></span>] [<span class="bold"><strong>-v</strong></span>]</code>
<p>
where "ex_rep_xxx" is either "ex_rep_mgr" or "ex_rep_base". The only
difference is that:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
specifying <span class="bold"><strong>-M</strong></span> or
<span class="bold"><strong>-C</strong></span> is optional for ex_rep_mgr,
but one of these options must be specified for ex_rep_base.
</p>
</li>
<li>
<p>
The <span class="bold"><strong>-n</strong></span> option is not supported
supported by ex_rep_mgr. That option specifies the number of
nodes in the replication group. When you use the Replication
Manager, this number is automatically determined for you.
</p>
</li>
</ul>
</div>
<p>
The options apply to either version of the program except where noted.
They are as follows:
</p>
<div class="variablelist">
<dl>
<dt>
<span class="term">
<span class="bold">
<strong>-h</strong>
</span>
</span>
</dt>
<dd>Specify a home directory for the database environment.</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-l</strong>
</span>
</span>
</dt>
<dd>Listen on local host "host" at port "port" for incoming connections.</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-M</strong>
</span>
</span>
</dt>
<dd>Configure this process as a master.</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-C</strong>
</span>
</span>
</dt>
<dd>Configure this process as a client.</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-r</strong>
</span>
</span>
</dt>
<dd>
Identifies the helper site used for joining the group.
</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-R</strong>
</span>
</span>
</dt>
<dd>
Identifies a remote peer to be used for joining the group. This
peer is used for syncing purposes. See
<a class="xref" href="rep_mastersync.html#rep_c2c_sync" title="Client-to-client synchronization">Client-to-client synchronization</a>
for more information.
</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-a</strong>
</span>
</span>
</dt>
<dd>
Specify repmgr acknowledgement policy of all or quorum. See
<a href="../api_reference/C/repmgrset_ack_policy.html" class="olink">DB_ENV->repmgr_set_ack_policy()</a> for more information (ex_rep_mgr
only.)
</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-b</strong>
</span>
</span>
</dt>
<dd>
Indicates that bulk transfer should be used. See <a class="xref" href="rep_bulk.html" title="Bulk transfer">Bulk transfer</a> for more
information.
</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-n</strong>
</span>
</span>
</dt>
<dd>
Specify the total number of sites in the replication group
(ex_rep_base only).
</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-p</strong>
</span>
</span>
</dt>
<dd>Set the
election priority. See
<a class="xref" href="rep_elect.html" title="Elections">Elections</a> for more
information.
</dd>
<dt>
<span class="term">
<span class="bold">
<strong>-v</strong>
</span>
</span>
</dt>
<dd>Indicates that additional informational and debugging output should be enabled.</dd>
</dl>
</div>
<p>A typical ex_rep_mgr session begins with a command such as the
following, to start a master:</p>
<pre class="programlisting">ex_rep_mgr -M -p 100 -h DIR1 -l localhost:30100</pre>
<p>and several clients:</p>
<pre class="programlisting">ex_rep_mgr -C -p 50 -h DIR2 -l localhost:30101 -r localhost:30100
ex_rep_mgr -C -p 10 -h DIR3 -l localhost:30102 -r localhost:30100
ex_rep_mgr -C -p 0 -h DIR4 -l localhost:30103 -r localhost:30100</pre>
<p>
In this example, the client with home directory DIR4 can never become a
master (its priority is 0). Both of the other clients can become
masters, but the one with home directory DIR2 is preferred. Priorities
are assigned by the application and should reflect the desirability of
having particular clients take over as master in the case that the
master fails.
</p>
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