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<p>
Beyond the basic functionality that we have discussed so far in
this book, there are several replication features that you
should understand. These are all optional to use, but provide
useful functionality under the right circumstances.
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These additional features are:
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<p>
When a replication group has a new master, all replicas must
synchronize with that master. This means they must ensure
that the contents of their local database(s) are identical
to that contained by the new master.
</p>
<p>
This synchronization process can result in quite a lot of
network activity. It can also put a large strain on the
master server, especially if is part of a large
replication group or if there is somehow a large difference between
the master's database(s) and the contents of its replicas.
</p>
<p>
It is therefore possible to delay synchronization for any
replica that discovers it has a new master. You would do
this so as to give the master time to synchronize other
replicas before proceeding with the delayed replicas.
</p>
<p>
To delay synchronization of a replica environment, you
specify
<span>
<code class="literal">DB_REP_CONF_DELAYCLIENT</code> to
<code class="methodname">DB_ENV->rep_set_config()</code>
and then specify <code class="literal">1</code> to the <code class="literal">onoff</code>
parameter. (Specify <code class="literal">0</code> to turn the feature off.)
</span>
</p>
<p>
If you use delayed synchronization, then you must manually
synchronize the replica at some future time. Until you do this, the replica is out of
sync with the master, and it will ignore all database changes forwarded to it from
the master.
</p>
<p>
You synchronize a delayed replica by calling
<code class="methodname">DB_ENV->rep_sync()</code>
on the replica that has been delayed.
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