问题 ;

  • 部署时如何知道自己是 broker 还是 NameServer
  • topic 订阅信息放在哪里
  • broker 的作用到底是什么
  • 纪录是如何持久化的
  • 群发的时候,是如何储存消息的
  • send 方法到底有没有使用多线程发送处理,简单叙述一个 send 的过程
  • transientStorePool 作用到底是什么
  • 为什么要使用堆外内存来存储消息先,而不是使用堆内内存

    以上几个问题,是在学习中思考的问题,我们将在学习过程中逐渐寻找答案。

概述

本文将会走完文件存储的主体流程,后续分析各个重要的类。下面简述来自参考资料,过程简述如下 :

SendMessageProcessor.processRequest
-->buildMsgContext(ctx, requestHeader);
-->this.executeSendMessageHookBefore(ctx, request, mqtraceContext);
-->sendMessage
(检查消息)
-->super.msgCheck(ctx, requestHeader, response);
(查询topic的配置信息)
-->this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());
(处理重试消息)
-->handleRetryAndDLQ(requestHeader, response, request, msgInner, topicConfig)
-->this.brokerController.getMessageStore().putMessage(msgInner);
-->this.commitLog.putMessage(msg);
-->this.mappedFileQueue.getLastMappedFile();
-->mappedFile.appendMessage(msg, this.appendMessageCallback);
(如果是同步刷盘则立即调用该方法刷盘)
-->handleDiskFlush(result, putMessageResult, msg);
-->异步刷盘的情况下通过唤起FlushRealTimeService的线程刷盘
(处理主从同步)
-->handleHA(result, putMessageResult, messageExtBatch);

源码分析

消息持久化几个重要的类 :

  • DefaultMessageStore
  • commitLog
  • MappedFile

DefaultMessageStore 持有 commitLog ,commitLog 持有 MappedFileQueue ,MappedFileQueue 管理着多个 MappedFile.

首先我们从 DefaultMessageStore 的 putMessage 方法

    /**
* 1. 判断是否条件满足条件
* 2. 调用 this.commitLog.putMessage(msg);
*
* @param msg Message instance to store
* @return
*/
public PutMessageResult putMessage(MessageExtBrokerInner msg) {
if (this.shutdown) {
log.warn("message store has shutdown, so putMessage is forbidden");
return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
} // 该 broker 是 slave 模式
if (BrokerRole.SLAVE == this.messageStoreConfig.getBrokerRole()) {
long value = this.printTimes.getAndIncrement();
if ((value % 50000) == 0) {
log.warn("message store is slave mode, so putMessage is forbidden ");
} return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
} if (!this.runningFlags.isWriteable()) {
long value = this.printTimes.getAndIncrement();
if ((value % 50000) == 0) {
log.warn("message store is not writeable, so putMessage is forbidden " + this.runningFlags.getFlagBits());
} return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
} else {
this.printTimes.set(0);
} if (msg.getTopic().length() > Byte.MAX_VALUE) {
log.warn("putMessage message topic length too long " + msg.getTopic().length());
return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, null);
} if (msg.getPropertiesString() != null && msg.getPropertiesString().length() > Short.MAX_VALUE) {
log.warn("putMessage message properties length too long " + msg.getPropertiesString().length());
return new PutMessageResult(PutMessageStatus.PROPERTIES_SIZE_EXCEEDED, null);
} if (this.isOSPageCacheBusy()) {
return new PutMessageResult(PutMessageStatus.OS_PAGECACHE_BUSY, null);
} long beginTime = this.getSystemClock().now();
//写入逻辑
PutMessageResult result = this.commitLog.putMessage(msg); long eclipseTime = this.getSystemClock().now() - beginTime;
if (eclipseTime > 500) {
log.warn("putMessage not in lock eclipse time(ms)={}, bodyLength={}", eclipseTime, msg.getBody().length);
}
this.storeStatsService.setPutMessageEntireTimeMax(eclipseTime); if (null == result || !result.isOk()) {
this.storeStatsService.getPutMessageFailedTimes().incrementAndGet();
} return result;
}

CommitLog 的 putMessage 方法

    /**
* @param msg
* @return
*/
public PutMessageResult putMessage(final MessageExtBrokerInner msg) {
// Set the storage time
msg.setStoreTimestamp(System.currentTimeMillis());
// Set the message body BODY CRC (consider the most appropriate setting
// on the client)
msg.setBodyCRC(UtilAll.crc32(msg.getBody()));
// Back to Results
AppendMessageResult result = null; StoreStatsService storeStatsService = this.defaultMessageStore.getStoreStatsService(); String topic = msg.getTopic();
int queueId = msg.getQueueId(); final int tranType = MessageSysFlag.getTransactionValue(msg.getSysFlag());
if (tranType == MessageSysFlag.TRANSACTION_NOT_TYPE
|| tranType == MessageSysFlag.TRANSACTION_COMMIT_TYPE) {
// Delay Delivery 延迟发送,将topic 换成 SCHEDULE_TOPIC , queueId 换成 延迟时间级别
// 这是并发消息消费重试关键的一步,下一章会重点探讨消息重试机制与定时消息的实现原理。
if (msg.getDelayTimeLevel() > 0) {
if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) {
msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel());
} topic = ScheduleMessageService.SCHEDULE_TOPIC;
queueId = ScheduleMessageService.delayLevel2QueueId(msg.getDelayTimeLevel()); // Backup real topic, queueId
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_TOPIC, msg.getTopic());
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_QUEUE_ID, String.valueOf(msg.getQueueId()));
msg.setPropertiesString(MessageDecoder.messageProperties2String(msg.getProperties())); msg.setTopic(topic);
msg.setQueueId(queueId);
}
} long eclipseTimeInLock = 0;
MappedFile unlockMappedFile = null;
MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile(); putMessageLock.lock(); //spin or ReentrantLock ,depending on store config 自旋或是重入锁看存储配置
try {
long beginLockTimestamp = this.defaultMessageStore.getSystemClock().now();
this.beginTimeInLock = beginLockTimestamp; // Here settings are stored timestamp, in order to ensure an orderly
// global
msg.setStoreTimestamp(beginLockTimestamp); if (null == mappedFile || mappedFile.isFull()) {
mappedFile = this.mappedFileQueue.getLastMappedFile(0); // Mark: NewFile may be cause noise
}
if (null == mappedFile) {
log.error("create mapped file1 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
beginTimeInLock = 0;
return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, null);
}
//核心逻辑!!可知 mappedFile是最终写入文件中的实施者
result = mappedFile.appendMessage(msg, this.appendMessageCallback);
switch (result.getStatus()) {
case PUT_OK:
break;
case END_OF_FILE:
unlockMappedFile = mappedFile;
// Create a new file, re-write the message
mappedFile = this.mappedFileQueue.getLastMappedFile(0);
if (null == mappedFile) {
// XXX: warn and notify me
log.error("create mapped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
beginTimeInLock = 0;
return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result);
}
result = mappedFile.appendMessage(msg, this.appendMessageCallback);
break;
case MESSAGE_SIZE_EXCEEDED:
case PROPERTIES_SIZE_EXCEEDED:
beginTimeInLock = 0;
return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, result);
case UNKNOWN_ERROR:
beginTimeInLock = 0;
return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result);
default:
beginTimeInLock = 0;
return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result);
} eclipseTimeInLock = this.defaultMessageStore.getSystemClock().now() - beginLockTimestamp;
beginTimeInLock = 0;
} finally {
putMessageLock.unlock();
} if (eclipseTimeInLock > 500) {
log.warn("[NOTIFYME]putMessage in lock cost time(ms)={}, bodyLength={} AppendMessageResult={}", eclipseTimeInLock, msg.getBody().length, result);
} if (null != unlockMappedFile && this.defaultMessageStore.getMessageStoreConfig().isWarmMapedFileEnable()) {
this.defaultMessageStore.unlockMappedFile(unlockMappedFile);
} PutMessageResult putMessageResult = new PutMessageResult(PutMessageStatus.PUT_OK, result); // Statistics
storeStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).incrementAndGet();
storeStatsService.getSinglePutMessageTopicSizeTotal(topic).addAndGet(result.getWroteBytes()); handleDiskFlush(result, putMessageResult, msg);
handleHA(result, putMessageResult, msg); return putMessageResult;
}

mappedFile 执行写入内存操作

    public AppendMessageResult appendMessage(final MessageExtBrokerInner msg, final AppendMessageCallback cb) {
return appendMessagesInner(msg, cb);
} public AppendMessageResult appendMessagesInner(final MessageExt messageExt, final AppendMessageCallback cb) {
assert messageExt != null;
assert cb != null; int currentPos = this.wrotePosition.get();
// 判断写针位置(是否已经大于文件大小)如果 currentPos 小于文件大小,通过 slice()方法创建一个与 MappedFile 的共享 内
//存区,并设置 position 为当前指针 。
if (currentPos < this.fileSize) {
// writeBuffer不为空则取 writeBuffer 剩下的空间,否则取 mappedByteBuffer 剩下的空间
// writeBuffer 的 赋值在 init 方法,构造时不使用 TransientStorePool ,writeBuffeer 为 null
ByteBuffer byteBuffer = writeBuffer != null ? writeBuffer.slice() : this.mappedByteBuffer.slice();
byteBuffer.position(currentPos);
AppendMessageResult result = null;
if (messageExt instanceof MessageExtBrokerInner) {
result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBrokerInner) messageExt);
} else if (messageExt instanceof MessageExtBatch) {
result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBatch) messageExt);
} else {
return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);
}
this.wrotePosition.addAndGet(result.getWroteBytes());
this.storeTimestamp = result.getStoreTimestamp();
return result;
}
log.error("MappedFile.appendMessage return null, wrotePosition: {} fileSize: {}", currentPos, this.fileSize);
return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);
}

CommitLog$DefaultAppendMessageCallback非静态内部类中的方法

        /**
* 1. 生成 messageId
* 2. 获取offset
* 3. 构造消息
* 4. buffer put 方法 ,后续会刷入文件
* @param fileFromOffset
* @param byteBuffer
* @param maxBlank
* @param msgInner
* @return
*/
public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank,
final MessageExtBrokerInner msgInner) {
// STORETIMESTAMP + STOREHOSTADDRESS + OFFSET <br> // 创建全局唯一消息ID
// PHY OFFSET
long wroteOffset = fileFromOffset + byteBuffer.position(); this.resetByteBuffer(hostHolder, 8);
String msgId = MessageDecoder.createMessageId(this.msgIdMemory, msgInner.getStoreHostBytes(hostHolder), wroteOffset); // Record ConsumeQueue information
keyBuilder.setLength(0);
keyBuilder.append(msgInner.getTopic());
keyBuilder.append('-');
keyBuilder.append(msgInner.getQueueId());
String key = keyBuilder.toString(); //获取该消息在消息队列的偏移量 。 CommitLog 中保存了当前所有消息队列的当
//前待写入偏移量 。
Long queueOffset = CommitLog.this.topicQueueTable.get(key);
if (null == queueOffset) {
queueOffset = 0L;
CommitLog.this.topicQueueTable.put(key, queueOffset);
} // Transaction messages that require special handling
// 需要特殊处理的事务消息
// 可以看到消息类型为 TRANSACTION_PREPARED_TYPE 或是 TRANSACTION_ROLLBACK_TYPE ,那么
// 偏移量改为 0L
final int tranType = MessageSysFlag.getTransactionValue(msgInner.getSysFlag());
switch (tranType) {
// Prepared and Rollback message is not consumed, will not enter the
// consumer queuec
case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
queueOffset = 0L;
break;
case MessageSysFlag.TRANSACTION_NOT_TYPE:
case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
default:
break;
} /**
* Serialize message
*/
final byte[] propertiesData =
msgInner.getPropertiesString() == null ? null : msgInner.getPropertiesString().getBytes(MessageDecoder.CHARSET_UTF8); final int propertiesLength = propertiesData == null ? 0 : propertiesData.length; if (propertiesLength > Short.MAX_VALUE) {
log.warn("putMessage message properties length too long. length={}", propertiesData.length);
return new AppendMessageResult(AppendMessageStatus.PROPERTIES_SIZE_EXCEEDED);
} final byte[] topicData = msgInner.getTopic().getBytes(MessageDecoder.CHARSET_UTF8);
final int topicLength = topicData.length; final int bodyLength = msgInner.getBody() == null ? 0 : msgInner.getBody().length; final int msgLen = calMsgLength(bodyLength, topicLength, propertiesLength); // Exceeds the maximum message
if (msgLen > this.maxMessageSize) {
CommitLog.log.warn("message size exceeded, msg total size: " + msgLen + ", msg body size: " + bodyLength
+ ", maxMessageSize: " + this.maxMessageSize);
return new AppendMessageResult(AppendMessageStatus.MESSAGE_SIZE_EXCEEDED);
} // Determines whether there is sufficient free space
if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) {
this.resetByteBuffer(this.msgStoreItemMemory, maxBlank);
// 1 TOTALSIZE
this.msgStoreItemMemory.putInt(maxBlank);
// 2 MAGICCODE
this.msgStoreItemMemory.putInt(CommitLog.BLANK_MAGIC_CODE);
// 3 The remaining space may be any value
// Here the length of the specially set maxBlank
final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
byteBuffer.put(this.msgStoreItemMemory.array(), 0, maxBlank);
return new AppendMessageResult(AppendMessageStatus.END_OF_FILE, wroteOffset, maxBlank, msgId, msgInner.getStoreTimestamp(),
queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills);
} // Initialization of storage space
this.resetByteBuffer(msgStoreItemMemory, msgLen);
// 1 TOTALSIZE
this.msgStoreItemMemory.putInt(msgLen);
// 2 MAGICCODE
this.msgStoreItemMemory.putInt(CommitLog.MESSAGE_MAGIC_CODE);
// 3 BODYCRC
this.msgStoreItemMemory.putInt(msgInner.getBodyCRC());
// 4 QUEUEID
this.msgStoreItemMemory.putInt(msgInner.getQueueId());
// 5 FLAG
this.msgStoreItemMemory.putInt(msgInner.getFlag());
// 6 QUEUEOFFSET
this.msgStoreItemMemory.putLong(queueOffset);
// 7 PHYSICALOFFSET
this.msgStoreItemMemory.putLong(fileFromOffset + byteBuffer.position());
// 8 SYSFLAG
this.msgStoreItemMemory.putInt(msgInner.getSysFlag());
// 9 BORNTIMESTAMP
this.msgStoreItemMemory.putLong(msgInner.getBornTimestamp());
// 10 BORNHOST
this.resetByteBuffer(hostHolder, 8);
this.msgStoreItemMemory.put(msgInner.getBornHostBytes(hostHolder));
// 11 STORETIMESTAMP
this.msgStoreItemMemory.putLong(msgInner.getStoreTimestamp());
// 12 STOREHOSTADDRESS
this.resetByteBuffer(hostHolder, 8);
this.msgStoreItemMemory.put(msgInner.getStoreHostBytes(hostHolder));
//this.msgBatchMemory.put(msgInner.getStoreHostBytes());
// 13 RECONSUMETIMES
this.msgStoreItemMemory.putInt(msgInner.getReconsumeTimes());
// 14 Prepared Transaction Offset
this.msgStoreItemMemory.putLong(msgInner.getPreparedTransactionOffset());
// 15 BODY
this.msgStoreItemMemory.putInt(bodyLength);
if (bodyLength > 0)
this.msgStoreItemMemory.put(msgInner.getBody());
// 16 TOPIC
this.msgStoreItemMemory.put((byte) topicLength);
this.msgStoreItemMemory.put(topicData);
// 17 PROPERTIES
this.msgStoreItemMemory.putShort((short) propertiesLength);
if (propertiesLength > 0)
this.msgStoreItemMemory.put(propertiesData); final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
// Write messages to the queue buffer
// msgStoreItemMemory :HeapByteBuffer byteBuffer DirectByteBuffer。将消息从堆内内存转移到堆外内存。
byteBuffer.put(this.msgStoreItemMemory.array(), 0, msgLen); AppendMessageResult result = new AppendMessageResult(AppendMessageStatus.PUT_OK, wroteOffset, msgLen, msgId,
msgInner.getStoreTimestamp(), queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills); switch (tranType) {
case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
break;
case MessageSysFlag.TRANSACTION_NOT_TYPE:
case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
// The next update ConsumeQueue information
CommitLog.this.topicQueueTable.put(key, ++queueOffset);
break;
default:
break;
}
return result;
}

补充

堆内内存(HeapByteBuffer)就是我们常说的垃圾回收那部分的内存,而堆外内存(DirectByteBuffer)则是计算机分配给某个进程的内存,位于堆外,那么使用堆外内存的优势是什么呢?

  1. 减少了垃圾回收

    堆外内存由于不在堆内,所以减少了垃圾会的工作,垃圾回收的时候会涨停其他工作。
  2. 减去了复制的操作。

    堆内在flush到远程时,会先复制到直接内存(非堆内存),然后在发送;而堆外内存相当于省略掉了这个工作。(这一点就是零拷贝的知识点)

注意事项 :

java.nio.DirectByteBuffer对象在创建过程中会先通过Unsafe接口直接通过os::malloc来分配内存,然后将内存的起始地址和大小存到java.nio.DirectByteBuffer对象里,这样就可以直接操作这些内存(即是说DirectByteBuffer 放着堆内对象的地址,当操作的时候实际是操作堆内对象)。这些内存只有在DirectByteBuffer回收掉之后才有机会被回收,因此如果这些对象大部分都移到了old,但是一直没有触发CMS GC或者Full GC,那么悲剧将会发生,因为你的物理内存被他们耗尽了,因此为了避免这种悲剧的发生,通过

-XX:MaxDirectMemorySize

来指定最大的堆外内存大小,当使用达到了阈值的时候将调用System.gc来做一次full gc,以此来回收掉没有被使用的堆外内存。摘自参考资料

总结

我们可以看到 RocketMQ 最主要就是利用映射文件的方法来提高读写效率。

参考资料

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