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<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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