protected BlockingQueue<IncomingMessageEnvelope> newBlockingQueue() {
    return new LinkedBlockingQueue<IncomingMessageEnvelope>();
  }
Initializes the metrics and in-memory buffer for the {@param systemStreamPartition}.
@param systemStreamPartition represents the input system stream partition.
samza-api/src/main/java/org/apache/samza/util/BlockingEnvelopeMap.java