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<h2 class="title" style="clear: both"><a id="heartbeats"></a>Managing Heartbeats</h2>
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<p>
If your replicated application experiences few updates,
it is possible for the replication group to lose a
master without noticing it. This is because normally a
replicated application only knows that a master has
gone missing when update activity causes messages to be
passed between the master and replicas.
</p>
<p>
To guard against this, you can configure a heartbeat.
The heartbeat must be configured for both the master
and each of the replicas.
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<p>
On the master, you configure the application to send a
heartbeat on a defined interval when it is otherwise
idle. Do this by using the
<span>
<code class="methodname">Environment.setReplicationTimeout()</code>
method.
You pass this method the
<code class="methodname">ReplicationTimeoutType.HEARTBEAT_SEND</code>
constant.
</span>
You must also provide the method a value representing the
period between heartbeats in microseconds. Note that the
heartbeat is sent only if the system is idle.
</p>
<p>
On the replica, you configure the application to listen
for a heartbeat. The time that you configure here is
the amount of time the replica will wait for some
message from the master (either the heartbeat or some
other message) before concluding that the connection is
lost. You do this using the
<span>
<code class="methodname">Environment.setReplicationTimeout()</code>
method.
You pass this method the
<code class="methodname">ReplicationTimeoutType.HEARTBEAT_MONITOR</code>
constant and a timeout value in microseconds.
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For best results, configure the heartbeat monitor for a
longer time interval than the heartbeat send interval.
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