In the following sections typical administrative tasks relating to the management of an OWLIM-Enterprise cluster instance are covered.
After the instantiation of a master node, worker nodes can be added using a JMX client application, e.g. jconsole. From the MBeans tab, select the bean associated with the master node to be modified. Each bean will be named: ReplicationCluster/ClusterInfo/<repository_id>
Worker nodes are removed using the removeClusterNode operation, which requires only the repository URL.
When a new worker node is attached to a master it will not be utilised until it is synchronised with the other worker nodes, i.e. the current state of the clustered repository must be replicated to the new worker node. During replication, a random up to date worker node is selected and used to replicate its state to any worker in the NEEDS_UPDATE state. If the AutoReplication attribute is set to true, then this will happen automatically as soon as a worker node is added.
After setting up a master node it will be in a read-only mode. This is the default state of the master and is also called 'hot-standby'. In this mode it can handle query requests and despatch these requests to all its attached worker nodes.
If a master node should fail completely then the most immediate effect will be that clients of the repository will start getting errors when trying to query or update the repository. If this should happen, a hot-swap/read-only master must be brought in to read-write mode and all query and update requests should be targeted to this master.
Description of possible values of the Status attribute.
The current Master node implementation automatically initiates replication when it detects any of the necessary conditions, such as an inconsistent state of a node with respect to the most recent update available (comparing the node's fingerprint, number of successful updates, number of statements etc). However, this can be disabled and replication can be initiated manually. Here are the steps to follow:
During normal operations, the master node keeps the cluster synchronised by adopting the approach described in Replication. However, if a worker node becomes out of synch with the rest of the cluster, perhaps because it was offline or unreachable due to network problems then the master node will detect this condition and proceed as follows:
There are other situations that can cause a worker node to become out of synch with the cluster, for example if an update is passed directly to a worker node, bypassing the master node altogether. In this situation, the master node will detect the problem and stop passing any read or update requests to the problem worker node. However, because the fingerprint of the worker will not match any known state of the cluster, the master node will not be able to bring the worker back in to synch with the cluster. In this situation, the best approach is to clear the history log of the master node(s) and if necessary restart the master. This will cause the master to choose the worker with the most recent update to use for replication to the other worker nodes that have a different fingerprint.
Make sure that Tomcat has been configured to expose the JMX interface using either JAVA_OPTS, CATALINA_OPTS or by configuring the Windows Tomcat monitor application, see section 3.3.2.
This directory will not exist until the Sesame war files have been deployed to the [WEBAPPS] directory AND Tomcat is running. If the war files have been deployed, but the directory does not exist, try restarting Tomcat.
Can not connect the Sesame console to the local Sesame server at http://localhost:8080/openrdf-sesame
Make sure that the Sesame war files have been deployed and that Tomcat is running. Restart Tomcat if necessary.
Make sure that the repository template file [BIGOWLIM]/templates/bigowlim.ttl has been copied to the 'templates' subdirectory of the Sesame console's data directory.
The Sesame console cannot find the OWLIM-Enterprise jar file. Make sure it was copied from [BIGOWLIM]/lib to the Sesame installation folder here: [SESAME]/lib
The Lucene jar file must be copied from the BigOWLIM distribution to the Sesame server's WEB-INF/lib directory. Restart Tomcat if necessary.
The tools.jar file from the Java Development Kit (JDK) must be on the classpath or alternatively copied to Sesame server's WEB-INF/lib directory.
The maximum heap space must be increased, i.e. Tomcat's Java virtual machine must be allowed to allocate more memory. This can be done by setting the environment variable 'CATALINA_OPTS' to include the desired value, e.g. -Xmx1024m
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