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<? extends DeletePolicy> 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<String/* topic */, ConcurrentHashMap<Integer/* partition */, MessageStore>> stores = new ConcurrentHashMap<String, ConcurrentHashMap<Integer, MessageStore>>();
//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<Pattern> topicsPatSet = new HashSet<Pattern>();
private final ConcurrentHashMap<Integer, ScheduledFuture<?>> unflushIntervalMap = new ConcurrentHashMap<Integer, ScheduledFuture<?>>();
//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<File> getDataDirSet(final MetaConfig metaConfig) throws IOException {
final Set<String> paths = new HashSet<String>();
// 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<File> fileSet = new HashSet<File>();
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<Callable<MessageStore>> tasks = new ArrayList<Callable<MessageStore>>();
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<MessageStore>() {
//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<Callable<MessageStore>> tasks) throws IOException, InterruptedException {
for (Callable<MessageStore> task : tasks) {
MessageStore messageStore;
try {
messageStore = task.call();
ConcurrentHashMap<Integer/* partition */, MessageStore> map = this.stores.get(messageStore.getTopic());
if (map == null) {
map = new ConcurrentHashMap<Integer, MessageStore>();
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<Callable<MessageStore>> tasks) throws InterruptedException {
CompletionService<MessageStore> completionService = new ExecutorCompletionService<MessageStore>(executor);
for (Callable<MessageStore> 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<Integer/* partition */, MessageStore> map = this.stores.get(messageStore.getTopic());
if (map == null) {
map = new ConcurrentHashMap<Integer, MessageStore>();
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<Integer/* partition */, MessageStore> 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<Integer/* partition */, MessageStore> 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<MessageStore> getMessageStoresByTopic(final String topic) {
final ConcurrentHashMap<Integer/* partition */, MessageStore> 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<Integer/* partition */, MessageStore> 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<Integer, MessageStore>();
final ConcurrentHashMap<Integer/* partition */, MessageStore> 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。