MetaQ技术内幕——源码分析(四)

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前面，我们已经把Broker存储最重要的一个类具体分析了一遍，接下来，我们分析一下其删除的策略。前面介绍过Messagestore采用的多文件存储的组织方式，而存储空间不可能无限大，得有一定的删除策略对其进行删除以腾出空间给新的消息。

 

MetaQ允许自定义删除策略，需要实现接口DeletePolicy，默认提供了两种删除策略：过期删除（DiscardDeletePolicy）和过期打包删除（ArchiveDeletePolicy）。DiscardDeletePolicy和ArchiveDeletePolicy都比较简单，DiscardDeletePolicy主要是对于超过一定时期的文件进行删除，ArchiveDeletePolicy则是先打包备份再删除。

 

自定义策略是如何被识别和使用的呢，MetaQ定义了DeletePolicyFactory，所有删除策略的实例都由DeletePolicyFactory提供，DeletePolicyFactory对外提供了注册机制，利用反射机制生成实例，每个自定义的删除策略都必须有一个无参构造，DeletePolicyFactory生成实例代码如下:

 

public static DeletePolicy getDeletePolicy(String values) {
        String[] tmps = values.split(",");
        String name = tmps[0];
        Class clazz = policyMap.get(name);
        if (clazz == null) {
            throw new UnknownDeletePolicyException(name);
        }
        try {
           //直接调用class的newInstance()方法，该方法必须要求有一个无参构造
            DeletePolicy deletePolicy = clazz.newInstance();
            String[] initValues = null;
            if (tmps.length >= 2) {
                initValues = new String[tmps.length - 1];
                System.arraycopy(tmps, 1, initValues, 0, tmps.length - 1);
            }
            deletePolicy.init(initValues);
            return deletePolicy;
        }
        catch (Exception e) {
            throw new MetamorphosisServerStartupException("New delete policy `" + name + "` failed", e);
        }
    }

DeletePolicy和MessageStore如何结合在一起的呢？则是粘合剂MessageStoreManager，MessageStoreManager是存储模块的管家，负责与其他模块联系，也是MessageStore管理器，管理所有的MessageStore以及其删除策略，MessageStoreManager也是要好好分析的一个类。

 

 

private final ConcurrentHashMap> stores = new ConcurrentHashMap>();
//前面的存储组织方式介绍过一个主题对应多一个分区，每个分区对应一个MessageStore实例，分区号使用数值来表示，stores就是按照该方式组织管理的
	private final MetaConfig metaConfig;
//参数配置
	private ScheduledThreadPoolExecutor scheduledExecutorService;// =
	// Executors.newScheduledThreadPool(2);
  //调度服务，对不同的MessageStore实例flush，将数据提到到硬盘
	private final DeletePolicy deletePolicy;
  //删除策略选择器，这里采用的一个topic对应一种策略，而不是一个MessageStore对应一个策略实例，一个策略实例在同一个topic的不同MessageStore实例间是重用的
	private DeletePolicySelector deletePolicySelector;
  
	public static final int HALF_DAY = 1000 * 60 * 60 * 12;
  //topic 集合
	private final Set topicsPatSet = new HashSet();

	private final ConcurrentHashMap> unflushIntervalMap = new ConcurrentHashMap>();
//前面曾介绍过MessageStore的提交方式有两种：组提交和定时提交，unflushIntervalMap是存放
//定时提交的任务
	private Scheduler scheduler;
//定时调度器，用于定时调度删除任务
	public MessageStoreManager(final MetaConfig metaConfig, final DeletePolicy deletePolicy) {
		this.metaConfig   = metaConfig;
		this.deletePolicy = deletePolicy;
//生成策略选择器
		this.newDeletePolicySelector();
//添加匿名监听器，监听topic列表变化，如果列表发生变化，则新增列表并重新生成选择器
		this.metaConfig.addPropertyChangeListener("topics", new PropertyChangeListener() {
			public void propertyChange(final PropertyChangeEvent evt) {
				MessageStoreManager.this.makeTopicsPatSet();
				MessageStoreManager.this.newDeletePolicySelector();
			}
		});
 //添加匿名监听，监听unflushInternal变化，如果发生变化
		this.metaConfig.addPropertyChangeListener("unflushInterval", new PropertyChangeListener() {
			public void propertyChange(final PropertyChangeEvent evt) {
				MessageStoreManager.this.scheduleFlushTask();
			}
		});
		this.makeTopicsPatSet();
      //初始化调度
		this.initScheduler();
		// 定时flush，该方法作者有详细注释就不在解释了
		this.scheduleFlushTask();
	}

 

MessageStoreManager实现接口Service，在启动是会调用init方法，关闭时调用dispose方法

public void init() {
		// 加载已有数据并校验
		try {
			this.loadMessageStores(this.metaConfig);
		} catch (final IOException e) {
			log.error("load message stores failed", e);
			throw new MetamorphosisServerStartupException("Initilize message store manager failed", e);
		} catch (InterruptedException e) {
			Thread.currentThread().interrupt();
		}
		this.startScheduleDeleteJobs();
	}

//
private Set getDataDirSet(final MetaConfig metaConfig) throws IOException {
		final Set paths = new HashSet();
		// public data path
      //公共数据目录
		paths.add(metaConfig.getDataPath());
		// topic data path
      //私有数据目录
		for (final String topic : metaConfig.getTopics()) {
			final TopicConfig topicConfig = metaConfig.getTopicConfig(topic);
			if (topicConfig != null) {
				paths.add(topicConfig.getDataPath());
			}
		}
		final Set fileSet = new HashSet();
		for (final String path : paths) {
			//验证数据目录是否存在
			fileSet.add(this.getDataDir(path));
		}
		return fileSet;
	}

private void loadMessageStores(final MetaConfig metaConfig) throws IOException, InterruptedException {
//加载数据目录列表，再加载每个目录下的数据
		for (final File dir : this.getDataDirSet(metaConfig)) {
			this.loadDataDir(metaConfig, dir);
		}
	}

	private void loadDataDir(final MetaConfig metaConfig, final File dir) throws IOException, InterruptedException {
		log.warn("Begin to scan data path:" + dir.getAbsolutePath());
		final long start = System.currentTimeMillis();
		final File[] ls = dir.listFiles();
		int nThreads = Runtime.getRuntime().availableProcessors() + 1;
		ExecutorService executor = Executors.newFixedThreadPool(nThreads);
		int count = 0;
      //将加载验证每个分区的数据包装成一个个任务
		List> tasks = new ArrayList>();
		for (final File subDir : ls) {
			if (!subDir.isDirectory()) {
				log.warn("Ignore not directory path:" + subDir.getAbsolutePath());
			} else {
				final String name = subDir.getName();
				final int index = name.lastIndexOf('-');
				if (index < 0) {
					log.warn("Ignore invlaid directory:" + subDir.getAbsolutePath());
					continue;
				}
	              //包装任务
				tasks.add(new Callable() {
					//回调方法，方法将具体的加载验证分区数据
@Override
					public MessageStore call() throws Exception {
						log.warn("Loading data directory:" + subDir.getAbsolutePath() + "...");
						final String topic = name.substring(0, index);
						final int partition = Integer.parseInt(name.substring(index + 1));                   //构造MessageStore实例的时候会自动加载验证数据，在初始化MessageStore实例的时候会给该MessageStore实例选择该topic的删除策略
						final MessageStore messageStore = new MessageStore(topic, partition, metaConfig,
								MessageStoreManager.this.deletePolicySelector.select(topic, MessageStoreManager.this.deletePolicy));
						return messageStore;
					}
				});
				count++;
				if (count % nThreads == 0 || count == ls.length) {
//如果配置了并行加载，则使用并行加载
					if (metaConfig.isLoadMessageStoresInParallel()) {
						this.loadStoresInParallel(executor, tasks);
					} else {
//串行加载验证数据
						this.loadStores(tasks);
					}
				}
			}
		}
		executor.shutdownNow();
		log.warn("End to scan data path in " + (System.currentTimeMillis() - start) / 1000 + " secs");
	}

 

在init方法中做的一件事情就是加载校验已有的数据，加载校验的方式有两种个，串行和并行。

//串行加载验证数据，则在主线程上完成验证加载工作，其缺点是较慢，好处是不会打乱日志顺序
private void loadStores(List> tasks) throws IOException, InterruptedException {
		for (Callable task : tasks) {
			MessageStore messageStore;
			try {
				messageStore = task.call();
				ConcurrentHashMap map = this.stores.get(messageStore.getTopic());
				if (map == null) {
					map = new ConcurrentHashMap();
					this.stores.put(messageStore.getTopic(), map);
				}
				map.put(messageStore.getPartition(), messageStore);
			} catch (IOException e) {
				throw e;
			} catch (InterruptedException e) {
				throw e;
			} catch (Exception e) {
				throw new IllegalStateException(e);
			}
		}
		tasks.clear();
	}

//并行加载数据，当数据过多的时候，启动并行加载数据可以加快启动速度；但是会打乱启动的日志顺序，默认不启用。
private void loadStoresInParallel(ExecutorService executor, List> tasks) throws InterruptedException {
		CompletionService completionService = new ExecutorCompletionService(executor);
		for (Callable task : tasks) {
			completionService.submit(task);
		}
		for (int i = 0; i < tasks.size(); i++) {
			try {
                //确保任务都已经运行完毕
				MessageStore messageStore = completionService.take().get();

				ConcurrentHashMap map = this.stores.get(messageStore.getTopic());
				if (map == null) {
					map = new ConcurrentHashMap();
					this.stores.put(messageStore.getTopic(), map);
				}
				map.put(messageStore.getPartition(), messageStore);
			} catch (ExecutionException e) {
				throw ThreadUtils.launderThrowable(e);
			}
		}
		tasks.clear();
	}

 

MessageStoreManager关闭时调用dispose方法，确保资源都正确释放。

public void dispose() {
 //关闭调度器和调度池
		this.scheduledExecutorService.shutdown();
		if (this.scheduler != null) {
			try {
				this.scheduler.shutdown(true);
			} catch (final SchedulerException e) {
				log.error("Shutdown quartz scheduler failed", e);
			}
		}
//确保每一个 MessageStore实例都正确关闭
		for (final ConcurrentHashMap subMap : MessageStoreManager.this.stores
				.values()) {
			if (subMap != null) {
				for (final MessageStore msgStore : subMap.values()) {
					if (msgStore != null) {
						try {
							msgStore.close();
						} catch (final Throwable e) {
							log.error("Try to run close  " + msgStore.getTopic() + "," + msgStore.getPartition() + " failed", e);
						}
					}
				}
			}
		}
//清空stores列表
		this.stores.clear();
	}

 

MessageStoreManager对外提供了获取的MessageStore的方法getMessageStore(final String topic, final int partition)和getOrCreateMessageStore(final String topic, final int partition) throws IOException。

getMessageStore()从stores列表查找对应的MessageStore，如果不存在则返回空；而getOrCreateMessage()则先检查对应的topic是否曾经配置，如果没有则抛出异常，如果有则判断stores是否已有MessageStore实例，如果没有，则生成MessageStore实例放入到stores列表并返回，如果有，则直接返回。

public MessageStore getMessageStore(final String topic, final int partition) {
		final ConcurrentHashMap map = this.stores.get(topic);
		if (map == null) {
//如果topic对应的MessageStore实例列表不存在，则直接返回null
			return null;
		}
		return map.get(partition);
	}

	Collection getMessageStoresByTopic(final String topic) {
		final ConcurrentHashMap map = this.stores.get(topic);
		if (map == null) {
			return Collections.emptyList();
		}
		return map.values();
	}

	public MessageStore getOrCreateMessageStore(final String topic, final int partition) throws IOException {
		return this.getOrCreateMessageStoreInner(topic, partition, 0);
	}

	public MessageStore getOrCreateMessageStore(final String topic, final int partition, final long offsetIfCreate) throws IOException {
		return this.getOrCreateMessageStoreInner(topic, partition, offsetIfCreate);
	}

	private MessageStore getOrCreateMessageStoreInner(final String topic, final int partition, final long offsetIfCreate) throws IOException {
      //判断topic是否可用，即是否在topicsPatSet列表中
		if (!this.isLegalTopic(topic)) {
			throw new IllegalTopicException("The server do not accept topic " + topic);
		}
//判断分区号是否正确
		if (partition < 0 || partition >= this.getNumPartitions(topic)) {
			log.warn("Wrong partition " + partition + ",valid partitions (0," + (this.getNumPartitions(topic) - 1) + ")");
			throw new WrongPartitionException("wrong partition " + partition);
		}
		ConcurrentHashMap map = this.stores.get(topic);
//如果topic对应的列表不存在，则生成列表，放进stores中
		if (map == null) {
			map = new ConcurrentHashMap();
			final ConcurrentHashMap oldMap = this.stores.putIfAbsent(topic, map);
			if (oldMap != null) {
				map = oldMap;
			}
		}
//判断列表中是否有存在分区号位partition为的MessageStore实例，如果有，直接返回；如果没有，则生成实例并放进列表中
		MessageStore messageStore = map.get(partition);
		if (messageStore != null) {
			return messageStore;
		} else {
			// 对string加锁，特例
			synchronized (topic.intern()) {
				messageStore = map.get(partition);
				// double check
				if (messageStore != null) {
					return messageStore;
				}
				messageStore = new MessageStore(topic, partition, this.metaConfig, this.deletePolicySelector.select(topic, this.deletePolicy), offsetIfCreate);
				log.info("Created a new message storage for topic=" + topic + ",partition=" + partition);
				map.put(partition, messageStore);
			}
		}
		return messageStore;
	}

	boolean isLegalTopic(final String topic) {
		for (final Pattern pat : this.topicsPatSet) {
			if (pat.matcher(topic).matches()) {
				return true;
			}
		}
		return false;
	}

通过MessageStoreManager，我们把MessageStore和删除策略很好的组织在一起，并在MessageStoreManager提供定时提交的功能，提升了数据的可靠性；通过MessageStoreManager也为其他模块访问存储模块提供了接口。

 

我觉得MessageStoreManager设计不好的地方在于topicsPatSet，在topic列表发生变化的时候，没有先清空topicsPatSet，而是直接添加，而且没有对topic对应的MessageStore实例进行重新初始化，如果MessageStore实例已经存在，新删除策略配置不能生效。个人建议是一旦topic列表发生变化的时候，重新初始化整个存储模块，保证一致性。

 

至此， Broker的消息存储模块基本分析完毕。下一篇，进入Broker网络相关以及消息处理流程分析。