@Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((partitionMetadata == null) ? 0 : partitionMetadata.hashCode());
    result = prime * result + ((streamName == null) ? 0 : streamName.hashCode());
    return result;
  }
@return A map of SystemStreamPartitionMetadata that includes offset
        information for each partition.
samza-api/src/main/java/org/apache/samza/system/SystemStreamMetadata.java