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<table width="100%" summary="Navigation header">
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<th colspan="3" align="center">Replication PRAGMAs</th>
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<td width="20%" align="left"><a accesskey="p" href="sqlrep.html">Prev</a> </td>
<th width="60%" align="center">Chapter 4. Using Replication with the SQL API</th>
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<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="reppragma"></a>Replication PRAGMAs</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="reppragma.html#pragma_replication">PRAGMA replication</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="reppragma.html#pragma_replication_initial_master">PRAGMA replication_initial_master</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="reppragma.html#pragma_replication_local_site">PRAGMA replication_local_site</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="reppragma.html#pragma_replication_remote_site">PRAGMA replication_remote_site</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="reppragma.html#pragma_replication_remove_site">PRAGMA replication_remove_site</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="reppragma.html#pragma_replication_verbose_output">PRAGMA replication_verbose_output</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="reppragma.html#pragma_replication_verbose_file">PRAGMA replication_verbose_file</a>
</span>
</dt>
</dl>
</div>
<p>
To control replication when using the Berkeley DB SQL
interface, you use the following PRAGMAs. For an example of
how to use these, see
<a class="xref" href="rep_usageexamples.html" title="Replication Usage Examples">Replication Usage Examples</a>.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="pragma_replication"></a>PRAGMA replication</h3>
</div>
</div>
</div>
<pre class="programlisting">PRAGMA replication=ON|OFF </pre>
<p>
Enables the local environment to participate in
replication.
</p>
<p>
Before invoking this PRAGMA for a brand new
database (one that has never been opened), you
must invoke the
<code class="literal">replication_local_site</code> PRAGMA
and then either the
<code class="literal">replication_initial_master</code> or
the <code class="literal">replication_remote_site</code>
PRAGMA. These actions define the way this site fits
into the replication group.
</p>
<p>
If you are enabling replication for an existing
database, it must become the initial master for a
new replication group. You must invoke the
<code class="literal">replication_local_site</code> PRAGMA
followed by the
<code class="literal">replication_initial_master</code>
PRAGMA before enabling replication.
</p>
<p>
If you use this PRAGMA to turn off replication,
then replication is completely disabled for the
environment. In order to enable replication again,
you follow the procedure used to enable replication
on an existing database; that is, invoke the
<code class="literal">replication_local_site</code> PRAGMA
followed by the
<code class="literal">replication_initial_master</code>
PRAGMA, followed by
<code class="literal">PRAGMA replication=ON</code>.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="pragma_replication_initial_master"></a>PRAGMA replication_initial_master</h3>
</div>
</div>
</div>
<pre class="programlisting">PRAGMA replication_initial_master=ON|OFF </pre>
<p>
Causes the local environment to start up as a
master site. This PRAGMA must be used once and only
once in the replicated lifetime of a BDB SQL
environment.
</p>
<p>
This PRAGMA is usually invoked for the first site in a
new replication group before the
<code class="literal">replication</code> PRAGMA is invoked
and before BDB SQL initially creates the underlying
BDB environment for a SQL database. Starting
replication on the initial master site establishes
the new replication group so that other sites can
join it.
</p>
<p>
However, you must call this PRAGMA
when enabling replication for a database that
already exists. Doing so causes the existing
database to become the replication master for a new
replication group.
</p>
<p>
Note that subsequent election activity can cause
other sites in the replication group to become
master. Do not assume that the initial master site
will remain master indefinitely, or that it will
rejoin the replication group as master after a
shutdown.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="pragma_replication_local_site"></a>PRAGMA replication_local_site</h3>
</div>
</div>
</div>
<pre class="programlisting">PRAGMA replication_local_site="hostname:port" </pre>
<p>
Sets the local site information for replication.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="pragma_replication_remote_site"></a>PRAGMA replication_remote_site</h3>
</div>
</div>
</div>
<pre class="programlisting">PRAGMA replication_remote_site="hostname:port" </pre>
<p>
Sets information about a remote helper site in the
replication group.
</p>
<p>
This PRAGMA is needed when a site first joins an
existing replication group to specify a site that
is already in the replication group. It must be
invoked before the <code class="literal">replication</code>
PRAGMA is invoked. This PRAGMA is not needed on
the initial master site or when restarting a site
that is already a member of the replication group.
However, supplying this PRAGMA in those situations
does no harm.
</p>
<p>
Note that the information provided to this PRAGMA
can be superseded by normal replication activity
over the course of the environment's lifetime.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="pragma_replication_remove_site"></a>PRAGMA replication_remove_site</h3>
</div>
</div>
</div>
<pre class="programlisting">PRAGMA replication_remove_site="hostname:port" </pre>
<p>
Removes the specified site from the replication group.
Use this PRAGMA if you truly want to remove the
site permanently from the group. It is not
desirable to call this PRAGMA if a site has been
temporarily shut down or disconnected from the rest
of the replication group.
</p>
<p>
Removing a site from the replication group means
that the site is no longer counted towards the
total number of sites belonging to the group. This
is important when the replication group requires
knowledge about whether a quorum has been reached
(such as when, for example, elections are held).
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="pragma_replication_verbose_output"></a>PRAGMA replication_verbose_output</h3>
</div>
</div>
</div>
<pre class="programlisting">PRAGMA replication_verbose_output=ON|OFF </pre>
<p>
If set to TRUE, additional logging information
specifically related to replication is created.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="pragma_replication_verbose_file"></a>PRAGMA replication_verbose_file</h3>
</div>
</div>
</div>
<pre class="programlisting">PRAGMA replication_verbose_file="filename" </pre>
<p>
Indicates that verbose replication output should be
sent to the specified file, as opposed to STDOUT.
</p>
</div>
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