Chapter 38. High Availability Using Server Hinting

In Red Hat JBoss Data Grid, Server Hinting ensures that backed up copies of data are not stored on the same physical server, rack, or data center as the original. Server Hinting does not apply to total replication because total replication mandates complete replicas on every server, rack, and data center.

Data distribution across nodes is controlled by the Consistent Hashing mechanism. JBoss Data Grid offers a pluggable policy to specify the consistent hashing algorithm. For details on configuring this policy refer to the ConsistentHashFactories section in the JBoss Data Grid Developer Guide .

Setting a machineId, rackId, or siteId in the transport configuration will trigger the use of TopologyAwareConsistentHashFactory, which is the equivalent of the DefaultConsistentHashFactory with Server Hinting enabled.

Server Hinting is particularly important when ensuring the high availability of your JBoss Data Grid implementation.

When setting up a clustered environment in Red Hat JBoss Data Grid, Server Hinting is configured when establishing JGroups configuration.

JBoss Data Grid ships with several JGroups files pre-configured for clustered mode. These files can be used as a starting point when configuring Server Hinting in JBoss Data Grid.

See Also: Pre-Configured JGroups Files

In Red Hat JBoss Data Grid’s Remote Client-Server mode, Server Hinting is configured in the JGroups subsystem on the transport element for the default stack, as follows:

<subsystem xmlns="urn:jboss:domain:jgroups:3.0"
	   default-stack="${jboss.default.jgroups.stack:udp}">
	<stack name="udp">
		<transport type="UDP"
			   socket-binding="jgroups-udp"
			   site="${jboss.jgroups.transport.site:s1}"
			   rack="${jboss.jgroups.transport.rack:r1}"
			   machine="${jboss.jgroups.transport.machine:m1}">
			   <!-- Additional configuration elements here -->
		</transport>
	</stack>
</subsystem>

<subsystem xmlns="urn:jboss:domain:jgroups:3.0"
	   default-stack="${jboss.default.jgroups.stack:udp}">
	<stack name="udp">
		<transport type="UDP"
			   socket-binding="jgroups-udp"
			   site="${jboss.jgroups.transport.site:s1}"
			   rack="${jboss.jgroups.transport.rack:r1}"
			   machine="${jboss.jgroups.transport.machine:m1}">
			   <!-- Additional configuration elements here -->
		</transport>
	</stack>
</subsystem>

In Red Hat JBoss Data Grid’s Library mode, Server Hinting is configured at the transport level. The following is a Server Hinting sample configuration:

<transport cluster = "MyCluster"
           machine = "LinuxServer01"
           rack = "Rack01"
           site = "US-WestCoast" />

<transport cluster = "MyCluster"
           machine = "LinuxServer01"
           rack = "Rack01"
           site = "US-WestCoast" />

The listed parameters are optional in a JBoss Data Grid configuration.

If machine, rack, or site are included in the configuration, TopologyAwareConsistentHashFactory is selected automatically, enabling Server Hinting. However, if Server Hinting is not configured, JBoss Data Grid’s distribution algorithms are allowed to store replications in the same physical machine/rack/data center as the original data.