| Interface | Description | 
|---|---|
| MasterAggregatorUsage | Master compute can access and change aggregators through this interface | 
| MasterGlobalCommUsage | All global master communication | 
| MasterGlobalCommUsageAggregators | Master compute can access reduce and broadcast methods
 through this interface, from masterCompute method. | 
| MasterObserver | Observer for Master. | 
| Class | Description | 
|---|---|
| AggregatorBroadcast<A extends org.apache.hadoop.io.Writable> | Writable representation of aggregated value | 
| AggregatorReduceOperation<A extends org.apache.hadoop.io.Writable> | Translates aggregation operation to reduce operations. | 
| AggregatorToGlobalCommTranslation | Class that translates aggregator handling on the master to
 reduce and broadcast operations supported by the MasterAggregatorHandler. | 
| BspServiceMaster<I extends org.apache.hadoop.io.WritableComparable,V extends org.apache.hadoop.io.Writable,E extends org.apache.hadoop.io.Writable> | ZooKeeper-based implementation of  CentralizedServiceMaster. | 
| DefaultMasterCompute | A dumb implementation of  MasterCompute. | 
| DefaultMasterObserver | A no-op implementation of MasterObserver to make it easier for users. | 
| MasterAggregatorHandler | Handler for reduce/broadcast on the master | 
| MasterCompute | Interface for defining a master vertex that can perform centralized
 computation between supersteps. | 
| MasterGlobalCommHandler | Handler for all master communications | 
| MasterInfo | Information about the master that is sent to other workers. | 
| MasterProgress | Stores information about master progress | 
| MasterThread<I extends org.apache.hadoop.io.WritableComparable,V extends org.apache.hadoop.io.Writable,E extends org.apache.hadoop.io.Writable> | Master thread that will coordinate the activities of the tasks. | 
| SuperstepClasses | Holds Computation and MessageCombiner class. | 
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