Using MapReduce in Cache

Note

This feature is only available in the NCache Enterprise Edition.

In order to use the MapReduce, initialize the MapReduce Task. Set the mapper, combiner and reducer factory to the task and then execute task on the cache.

Prerequisites

.NET/.NET Core

To learn about the standard prerequisites required to work with all NCache server-side features please refer to the given page on Server Side API Prerequisites.
For API details refer to: ICache, MapReduceTask, Combiner, Mapper, Reducer, ITrackableTask, GetResult, ITaskResult, IExecutionService, ExecuteTask, GetEnumerator.

The following example shows the sample usage of the MapReduce.

try
{
    // Pre-condition: Cache is already connected

    // Initialize MapReduce Task
    MapReduceTask task = new MapReduceTask();

    // Set Mapper, Combiner factory and Reducer factory
    task.Mapper = new ProductCountMapper();
    task.Combiner = new ProductCountCombinerFactory();
    task.Reducer = new ProductCountReducerFactory();

    // Execute task on cache
    ITrackableTask wordCount = cache.ExecutionService.ExecuteTask(task, new ProductCountKeyFilter());

    // Get result
    ITaskResult result = wordCount.GetResult();

    IDictionaryEnumerator enumResult = result.GetEnumerator();

    while (enumResult.MoveNext())
    {
        // Perform operations
    }
}
catch(OperationFailedException ex)
{
    if (ex.ErrorCode == NCacheErrorCodes.TASK_IN_SUBMISSION_FAILED_NODE)
    {
        // Task is failed during submission
        // Make sure that the mapper is defined 
    }
    else if (ex.ErrorCode == NCacheErrorCodes.TASK_STARTING_FAILED)
    {
        // Task is failed while starting
        // Make sure that the mapper is defined
    }
    else if (ex.ErrorCode == NCacheErrorCodes.TASK_CANT_BE_SUBMITTED)
    {
        // The limit of tasks to be submitted has been reached
        // No more task can be submitted
    }
    else if (ex.ErrorCode == NCacheErrorCodes.TASK_CANCELLED_REASON)
    {       
        // Task was cacelled and could not be submitted
    }
    else if (ex.ErrorCode == NCacheErrorCodes.TASK_SUBMISSION_FAILED)
    {
        // Task has failed to be submitted
    }
    else
    {
        // Exception can occur due to:
        // Connection Failures
        // Operation Timeout
        // Operation performed during state transfer
    }
}
catch (Exception ex)
{
    // Any generic exception like ArgumentNullException or ArgumentException
}

Using MapReduce in Cache

Note

Prerequisites

See Also