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<div class="chapter" lang="en" xml:lang="en">
<div class="titlepage">
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<div>
<h2 class="title"><a id="repapp"></a>Chapter 3. The DB Replication Manager</h2>
</div>
</div>
</div>
<div class="toc">
<p>
<b>Table of Contents</b>
</p>
<dl>
<dt>
<span class="sect1">
<a href="repapp.html#repmgr_grpmgmt">The DB_SITE Handle</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="rep_init_code.html">
Starting and Stopping Replication
</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="rep_init_code.html#election_flags">Managing Election Policies</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="rep_init_code.html#thread_count">Selecting the Number of Threads</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="repmgr_init_example_c.html">Adding the Replication Manager to
<span>ex_rep_gsg_simple</span>
</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="fwrkpermmessage.html">Permanent Message Handling</a>
</span>
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<dd>
<dl>
<dt>
<span class="sect2">
<a href="fwrkpermmessage.html#fmwrkpermpolicy">Identifying Permanent Message Policies</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="fwrkpermmessage.html#fmwrkpermtimeout">Setting the Permanent Message Timeout</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="fwrkpermmessage.html#perm2fmwrkexample">Adding a Permanent Message Policy to
<span>ex_rep_gsg_repmgr</span>
</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="electiontimes.html">Managing Election Times</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="electiontimes.html#electiontimeout">Managing Election Timeouts</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="electiontimes.html#electretrytime">Managing Election Retry Times</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="fmwrkconnectretry.html">Managing Connection Retries</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="heartbeats.html">Managing Heartbeats</a>
</span>
</dt>
</dl>
</div>
<p>
The easiest way to add replication to your transactional
application is to use the Replication Manager. The Replication Manager provides a comprehensive
communications layer that enables replication. For a brief listing
of the Replication Manager's feature set, see
<a class="xref" href="apioverview.html#repframeworkoverview" title="Replication Manager Overview">Replication Manager Overview</a>.
</p>
<p>
To use the Replication Manager, you make use of a combination of the
<code class="classname">DB_SITE</code>
class and related methods, plus special methods off the
<span><code class="classname">DB_ENV</code> class.</span>
That is:
</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>
Create an environment handle as normal.
</p>
</li>
<li>
<p>
Configure your environment handle as needed (e.g. set the
error file and error prefix values, if desired).
</p>
</li>
<li>
<p>
Use the Replication Manager replication classes and methods to configure
the Replication Manager. Using these classes and methods causes DB
to know that you are using the Replication Manager.
</p>
<p>
Configuring the Replication Manager entails setting the replication
environment's priority, setting the TCP/IP address that
this replication environment will use for incoming
replication messages, identifying TCP/IP addresses of other
replication environments, setting the number of replication
environments in the replication group, and so forth. These
actions are discussed throughout the remainder of this
chapter.
</p>
</li>
<li>
<p>
Open your environment handle. When you do this, be sure to
specify
<span>
<code class="literal">DB_INIT_REP</code> and
<code class="literal">DB_THREAD</code> to your open flags. (This
is in addition to the flags that you normally use for a
single-threaded transactional application). The first
of these causes replication to be initialized for the
application. The second causes your environment handle
to be free-threaded (thread safe). Both flags are
required for Replication Manager usage.
</span>
</p>
</li>
<li>
<p>
Start replication by calling
<span><code class="methodname">DB_ENV->repmgr_start()</code>.</span>
</p>
</li>
<li>
<p>
Open your databases as needed. Masters must open their databases
for read and write activity. Replicas can open their databases
for read-only activity, but doing so means they must
re-open the databases if the replica ever becomes a master.
Either way, replicas should never attempt to write to the
database(s) directly.
</p>
</li>
</ol>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
The Replication Manager allows you to only use one environment handle per
process.
</p>
</div>
<p>
When you are ready to shut down your application:
</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>
Close any open
<code class="classname">DB_SITE</code>
handles that you might have open.
</p>
</li>
<li>
<p>
Close your databases
</p>
</li>
<li>
<p>
Close your environment. This causes replication to stop as
well.
</p>
</li>
</ol>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
Before you can use the Replication Manager, you may have to enable it
in your DB library. This is
<span class="emphasis"><em>not</em></span> a requirement for Microsoft
Windows systems, or Unix systems that use pthread
mutexes by default. Other systems, notably BSD and
BSD-derived systems (such as Mac OS X), must enable the
Replication Manager when you configure the DB build.
</p>
<p>
You do this by <span class="emphasis"><em>not</em></span> disabling
replication and by configuring the library with POSIX
threads support. In other words, replication must be
turned on in the build (it is by default), and POSIX
thread support must be enabled if it is not already by
default. To do this, use the
<code class="literal">--enable-pthread_api</code> switch on the
configure script.
</p>
<p>
For example:
</p>
<pre class="programlisting">../dist/configure --enable-pthread-api</pre>
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="repmgr_grpmgmt"></a>The DB_SITE Handle</h2>
</div>
</div>
</div>
<p>
Before continuing, it is useful to mention the
<code class="classname">DB_SITE</code>
handle. This class is used to configure important attributes about
a site such as its host name and port number, and whether it is the
local site. It is also used to indicate whether a site is a
<span class="emphasis"><em>group creator</em></span>, which is important when you are
starting the very first site in a replication group for the very
first time.
</p>
<p>
The
<code class="classname">DB_SITE</code>
handle is used whenever you start up a site. It must be closed
before you close your
<code class="classname">DB_ENV</code>
handle.
</p>
<p>
The
<code class="classname">DB_SITE</code>
handle is plays an important role in replication group management. This topic
is fully described in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>.
</p>
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