@Override
  public int getScanQueueLength() {
    int length = 0;
    for (int i = numWriteQueues + numReadQueues; i
        < (numWriteQueues + numReadQueues + numScanQueues); i++) {
      length += queues.get(i).size();
    }
    return length;
  }
RPC Executor that uses different queues for reads and writes. With the options to use different
queues/executors for gets and scans. Each handler has its own queue and there is no stealing.
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/RWQueueRpcExecutor.java