protected int computeNumCallQueues(final int handlerCount, final float callQueuesHandlersFactor) {
    return Math.max(1, Math.round(handlerCount * callQueuesHandlersFactor));
  }
The default, 'fifo', has the least friction but is dumb. If set to 'deadline', uses a priority
queue and de-prioritizes long-running scans. Sorting by priority comes at a cost, reduced
throughput.
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/RpcExecutor.java