kafka broker的网络模型

生产环境出现了kafka接收到消息后，落盘延时的情况，所以研究下，kafka的网络模型，看一些源码:

Socketserver部分

看一下他的startup方法：

/**
   * Start the socket server
   */
  def startup() {
    val quotas = new ConnectionQuotas(maxConnectionsPerIp, maxConnectionsPerIpOverrides)
    for(i <- 0 until numProcessorThreads) {
      processors(i) = new Processor(i, 
                                    time, 
                                    maxRequestSize, 
                                    aggregateIdleMeter,
                                    newMeter("IdlePercent", "percent", TimeUnit.NANOSECONDS, Map("networkProcessor" -> i.toString)),
                                    numProcessorThreads, 
                                    requestChannel,
                                    quotas,
                                    connectionsMaxIdleMs)
      //启动processor
      Utils.newThread("kafka-network-thread-%d-%d".format(port, i), processors(i), false).start()
    }

    newGauge("ResponsesBeingSent", new Gauge[Int] {
      def value = processors.foldLeft(0) { (total, p) => total + p.countInterestOps(SelectionKey.OP_WRITE) }
    })

    // register the processor threads for notification of responses
    //监听来自requestChannel的相应。
    requestChannel.addResponseListener((id:Int) => processors(id).wakeup())

    // start accepting connections
    //启动一个acceptor线程用于监听新的连接
    this.acceptor = new Acceptor(host, port, processors, sendBufferSize, recvBufferSize, quotas)
    Utils.newThread("kafka-socket-acceptor", acceptor, false).start()
    acceptor.awaitStartup
    info("Started")
  }

• acceptor

  /**
   * Accept loop that checks for new connection attempts
   */
  def run() {
    serverChannel.register(selector, SelectionKey.OP_ACCEPT);
    startupComplete()
    var currentProcessor = 0
    while(isRunning) {
      val ready = selector.select(500)
      if(ready > 0) {
        val keys = selector.selectedKeys()
        val iter = keys.iterator()
        while(iter.hasNext && isRunning) {
          var key: SelectionKey = null
          try {
            key = iter.next
            iter.remove()
            if(key.isAcceptable)
               accept(key, processors(currentProcessor))
            else
               throw new IllegalStateException("Unrecognized key state for acceptor thread.")

            // round robin to the next processor thread
            // 采用轮询的方式将key（serverSocketChannel）分配给currentProcessor
            currentProcessor = (currentProcessor + 1) % processors.length
          } catch {
            case e: Throwable => error("Error while accepting connection", e)
          }
        }
      }
    }
    debug("Closing server socket and selector.")
    swallowError(serverChannel.close())
    swallowError(selector.close())
    shutdownComplete()
  }
  
  

}

• processor
  将新的连接放入队列中newConnections 就是一个ConcurrentLinkedQueue

  /**
   * Queue up a new connection for reading
   */
  def accept(socketChannel: SocketChannel) {
    newConnections.add(socketChannel)
    wakeup()
  }

/**
   * Register any new connections that have been queued up
   */
从队列中取出socketChannel，注册selector进行监听
private def configureNewConnections() {
    while(newConnections.size() > 0) {
      val channel = newConnections.poll()
      debug("Processor " + id + " listening to new connection from " + channel.socket.getRemoteSocketAddress)
      channel.register(selector, SelectionKey.OP_READ)
    }
  }