29.4. Distributed Task Failover

Red Hat JBoss Data Grid's distributed execution framework supports task failover in the following cases:
  • Failover due to a node failure where a task is executing.
  • Failover due to a task failure; for example, if a Callable task throws an exception.
The failover policy is disabled by default, and Runnable, Callable, and DistributedCallable tasks fail without invoking any failover mechanism.
JBoss Data Grid provides a random node failover policy, which will attempt to execute a part of a Distributed task on another random node if one is available.
A random failover execution policy can be specified using the following as an example:

Example 29.3. Random Failover Execution Policy

DistributedExecutorService des = new DefaultExecutorService(cache);
DistributedTaskBuilder<Boolean> taskBuilder = des.createDistributedTaskBuilder(new SomeCallable());
taskBuilder.failoverPolicy(DefaultExecutorService.RANDOM_NODE_FAILOVER);
DistributedTask<Boolean> distributedTask = taskBuilder.build();
Future<Boolean> future = des.submit(distributedTask);
Boolean r = future.get();
The DistributedTaskFailoverPolicy interface can also be implemented to provide failover management.

Example 29.4. Distributed Task Failover Policy Interface

/**
 * DistributedTaskFailoverPolicy allows pluggable fail over target selection for a failed remotely
 * executed distributed task.
 *
 */
public interface DistributedTaskFailoverPolicy {
 
   /**
    * As parts of distributively executed task can fail due to the task itself throwing an exception
    * or it can be an Infinispan system caused failure (e.g node failed or left cluster during task
    * execution etc).
    *
    * @param failoverContext
    *           the FailoverContext of the failed execution
    * @return result the Address of the Infinispan node selected for fail over execution
    */
   Address failover(FailoverContext context);
 
   /**
    * Maximum number of fail over attempts permitted by this DistributedTaskFailoverPolicy
    *
    * @return max number of fail over attempts
    */
   int maxFailoverAttempts();
}
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