1. Kafka.scala
在Kafka的main入口中startup KafkaServerStartable, 而KafkaServerStartable这是对KafkaServer的封装
1: val kafkaServerStartble = new KafkaServerStartable(serverConfig)
2: kafkaServerStartble.startup
1: package kafka.server
2: class KafkaServerStartable(val serverConfig: KafkaConfig) extends Logging {
3: private var server : KafkaServer = null
4:
5: private def init() {
6: server = new KafkaServer(serverConfig)
7: }
8:
9: def startup() {
10: try {
11: server.startup()
12: }
13: catch {...}
14: }
15: }
2. KafkaServer
KafkaServer代表一个kafka broker, 这是kafka的核心.
只需要看看里面startup了哪些modules, 就知道broker做了哪些工作, 后面一个个具体分析吧
1: package kafka.server
2: /**
3: * Represents the lifecycle of a single Kafka broker. Handles all functionality required
4: * to start up and shutdown a single Kafka node.
5: */
6: class KafkaServer(val config: KafkaConfig, time: Time = SystemTime) extends Logging {
7: var socketServer: SocketServer = null
8: var requestHandlerPool: KafkaRequestHandlerPool = null
9: var logManager: LogManager = null
10: var kafkaHealthcheck: KafkaHealthcheck = null
11: var topicConfigManager: TopicConfigManager = null
12: var replicaManager: ReplicaManager = null
13: var apis: KafkaApis = null
14: var kafkaController: KafkaController = null
15: val kafkaScheduler = new KafkaScheduler(config.backgroundThreads)
16: var zkClient: ZkClient = null
17:
18: /**
19: * Start up API for bringing up a single instance of the Kafka server.
20: * Instantiates the LogManager, the SocketServer and the request handlers - KafkaRequestHandlers
21: */
22: def startup() {
23: /* start scheduler */
24: kafkaScheduler.startup()
25:
26: /* setup zookeeper */
27: zkClient = initZk()
28:
29: /* start log manager */
30: logManager = createLogManager(zkClient)
31: logManager.startup()
32:
33: socketServer = new SocketServer(config.brokerId,
34: config.hostName,
35: config.port,
36: config.numNetworkThreads,
37: config.queuedMaxRequests,
38: config.socketSendBufferBytes,
39: config.socketReceiveBufferBytes,
40: config.socketRequestMaxBytes)
41: socketServer.startup()
42:
43: replicaManager = new ReplicaManager(config, time, zkClient, kafkaScheduler, logManager, isShuttingDown)
44: kafkaController = new KafkaController(config, zkClient)
45:
46: /* start processing requests */
47: apis = new KafkaApis(socketServer.requestChannel, replicaManager, zkClient, config.brokerId, config, kafkaController)
48: requestHandlerPool = new KafkaRequestHandlerPool(config.brokerId, socketServer.requestChannel, apis, config.numIoThreads)
49:
50: replicaManager.startup()
51:
52: kafkaController.startup()
53:
54: topicConfigManager = new TopicConfigManager(zkClient, logManager)
55: topicConfigManager.startup()
56:
57: /* tell everyone we are alive */
58: kafkaHealthcheck = new KafkaHealthcheck(config.brokerId, config.advertisedHostName, config.advertisedPort, config.zkSessionTimeoutMs, zkClient)
59: kafkaHealthcheck.startup()
60: }
2.1 KafkaScheduler
KafkaSchduler用于在后台执行一些任务，用ScheduledThreadPoolExecutor实现
1: package kafka.utils
2:
3: /**
4: * A scheduler based on java.util.concurrent.ScheduledThreadPoolExecutor
5: *
6: * It has a pool of kafka-scheduler- threads that do the actual work.
7: *
8: * @param threads The number of threads in the thread pool
9: * @param threadNamePrefix The name to use for scheduler threads. This prefix will have a number appended to it.
10: * @param daemon If true the scheduler threads will be "daemon" threads and will not block jvm shutdown.
11: */
12: @threadsafe
13: class KafkaScheduler(val threads: Int,
14: val threadNamePrefix: String = "kafka-scheduler-",
15: daemon: Boolean = true) extends Scheduler with Logging {
16: @volatile private var executor: ScheduledThreadPoolExecutor = null
17: override def startup() {
18: this synchronized {
19: executor = new ScheduledThreadPoolExecutor(threads) //创建ScheduledThreadPoolExecutor
20: executor.setContinueExistingPeriodicTasksAfterShutdownPolicy(false)
21: executor.setExecuteExistingDelayedTasksAfterShutdownPolicy(false)
22: executor.setThreadFactory(new ThreadFactory() {
23: def newThread(runnable: Runnable): Thread =
24: Utils.newThread(threadNamePrefix + schedulerThreadId.getAndIncrement(), runnable, daemon)
25: })
26: }
27: }
28:
29: def schedule(name: String, fun: ()=>Unit, delay: Long, period: Long, unit: TimeUnit) = {
30: val runnable = new Runnable { //将fun封装成Runnable
31: def run() = {
32: try {
33: fun()
34: } catch {...}
35: finally {...}
36: }
37: }
38: if(period >= 0) //在pool中进行delay schedule
39: executor.scheduleAtFixedRate(runnable, delay, period, unit)
40: else
41: executor.schedule(runnable, delay, unit)
42: }
2.2 Zookeeper Client
由于Kafka是基于zookeeper进行配置管理的， 所以需要创建zkclient和zookeeper集群通信
2.3 logManager
The entry point to the kafka log management subsystem. The log manager is responsible for log creation, retrieval, and cleaning.
Apache Kafka源码分析 – Log Management
2.4 ReplicaManager
在0.8中新加入的replica相关模块
Apache Kafka Replication Design – High level
kafka Detailed Replication Design V3
Apache Kafka源码分析 – ReplicaManager
2.5 Kafka Socket Server
首先broker server是socket server，所有和broker的交互都是通过往socket端口发送request来实现的
socketServer = new SocketServer(config.brokerId...)
KafkaApis
该类封装了所有request的处理逻辑
KafkaRequestHandler
2.6 offsetManager
offsetManager = createOffsetManager()
定期清除过期的offset数据，即compact操作，
scheduler.schedule(name = "offsets-cache-compactor", fun = compact, period = config.offsetsRetentionCheckIntervalMs, unit = TimeUnit.MILLISECONDS)
以及consumer相关的一些offset操作，不细究了，因为我们不用highlevel consumer
2.7 KafkaController
kafkaController = new KafkaController(config, zkClient, brokerState)
0.8后，为了处理replica，会用一个broker作为master，即controller，用于协调replica的一致性
2.8 TopicConfigManager
topicConfigManager = new TopicConfigManager(zkClient, logManager)
TopicConfigManager用于处理topic config的change，kafka除了全局的配置，还有一种叫Topic-level configuration
> bin/kafka-topics.sh --zookeeper localhost:2181 --alter --topic my-topic
--config max.message.bytes=128000
比如你可以这样设置，那么这些topic config如何生效的？
topic-level config默认是被存储在，
/brokers/topics/<topic_name>/config
但是topic很多的情况下，为了避免创建太多的watcher，
所以单独创建一个目录
/brokers/config_changes
来触发配置的变化
所以上面的命令除了，把配置写入topic/config，还有增加一个通知，告诉watcher哪个topic的config发生了变化
/brokers/config_changes/config_change_13321
并且这个通知有个suffix，用于区别是否已处理过
/** * Process the given list of config changes */ private def processConfigChanges(notifications: Seq[String]) { if (notifications.size > 0) { info("Processing config change notification(s)...") val now = time.milliseconds val logs = logManager.logsByTopicPartition.toBuffer val logsByTopic = logs.groupBy(_._1.topic).mapValues(_.map(_._2)) for (notification <- notifications) { val changeId = changeNumber(notification) if (changeId > lastExecutedChange) { //未处理过 val changeZnode = ZkUtils.TopicConfigChangesPath + "/" + notification val (jsonOpt, stat) = ZkUtils.readDataMaybeNull(zkClient, changeZnode) if(jsonOpt.isDefined) { val json = jsonOpt.get val topic = json.substring(1, json.length - 1) // hacky way to dequote，从通知中获取topic name if (logsByTopic.contains(topic)) { /* combine the default properties with the overrides in zk to create the new LogConfig */ val props = new Properties(logManager.defaultConfig.toProps) props.putAll(AdminUtils.fetchTopicConfig(zkClient, topic)) val logConfig = LogConfig.fromProps(props) for (log <- logsByTopic(topic)) log.config = logConfig //真正的更新log配置 info("Processed topic config change %d for topic %s, setting new config to %s.".format(changeId, topic, props)) purgeObsoleteNotifications(now, notifications) //删除过期的notification，10分钟 } } lastExecutedChange = changeId } } } }
并且broker重启后是会从zk中， loading完整的配置的，所以也ok的，这个主要用于实时更新topic的配置
2.8 KafkaHealthcheck
kafkaHealthcheck = new KafkaHealthcheck(config.brokerId, config.advertisedHostName, config.advertisedPort, config.zkSessionTimeoutMs, zkClient)
这个很简单，就像注释的，告诉所有人我还活着。。。
实现就是在，
/brokers/[0...N] --> advertisedHost:advertisedPort
register一个ephemeral znode，当SessionExpired时，再去register，典型zk应用
所以只需要watch这个路径就是知道broker是否还活着
2.9 ContolledShutdown
对于0.8之前，broker的startup和shutdown都很简单，把上面这些组件初始化，或stop就可以了
但是0.8后，增加replica，所以broker不能自己直接shutdown，需要先通知controller，controller做完处理后，比如partition leader的迁移，或replica offline，然后才能shutdown
private def controlledShutdown()
挺长的，逻辑就是找到controller，发送ControlledShutdownRequest，然后等待返回，如果失败，就是unclean shutdown
本文章摘自博客园，原文发布日期： 2014-02-14
