这篇文章主要为大家展示了“RocketMQ中broker消息存储之如何添加消息”，内容简而易懂，条理清晰，希望能够帮助大家解决疑惑，下面让小编带领大家一起研究并学习一下“RocketMQ中broker消息存储之如何添加消息”这篇文章吧。
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broker存储子系统追加消息的入口是DefaultMessageStore.asyncPutMessage，该方法会调用CommitLog.asyncPutMessage，主要实现如下：
// CommitLog.java public CompletableFutureasyncPutMessage(final MessageExtBrokerInner msg) { // msg准备... // 1. 获取最后一个block，准备写入 MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile(); putMessageLock.lock(); //spin or ReentrantLock ,depending on store config try { //.... if (null == mappedFile || mappedFile.isFull()) { // 加锁后重试一次，尝试新建一个block mappedFile = this.mappedFileQueue.getLastMappedFile(0); // Mark: NewFile may be cause noise } if (null == mappedFile) { // 新建block失败，返回 log.error("create mapped file1 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString()); beginTimeInLock = 0; return CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, null)); } // 2. append到block末尾 result = mappedFile.appendMessage(msg, this.appendMessageCallback); switch (result.getStatus()) { case PUT_OK: break; case END_OF_FILE: // 3. block剩余空间不足，新建下一个block，再次尝试写入 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 CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result)); } result = mappedFile.appendMessage(msg, this.appendMessageCallback); break; // 发送错误，失败返回... } // ... } finally { putMessageLock.unlock(); } // 4. 提交刷盘请求 CompletableFuture flushResultFuture = submitFlushRequest(result, putMessageResult, msg); // 5. 提交同步请求 CompletableFuture replicaResultFuture = submitReplicaRequest(result, putMessageResult, msg); return flushResultFuture.thenCombine(replicaResultFuture, (flushStatus, replicaStatus) -> { if (flushStatus != PutMessageStatus.PUT_OK) { putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT); } if (replicaStatus != PutMessageStatus.PUT_OK) { putMessageResult.setPutMessageStatus(replicaStatus); } return putMessageResult; }); }
MappedFile在执行数据追加时实际调用的是MappedFile.appendMessagesInner方法：
// MappedFile
public AppendMessageResult appendMessagesInner(final MessageExt messageExt, final AppendMessageCallback cb) {
assert messageExt != null;
assert cb != null;
int currentPos = this.wrotePosition.get();
if (currentPos < this.fileSize) {
ByteBuffer byteBuffer = writeBuffer != null ? writeBuffer.slice() : this.mappedByteBuffer.slice();
byteBuffer.position(currentPos);
AppendMessageResult result;
// 调用callback执行实际的数据写入，callback实现决定了数据的存储格式
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);
}msg实际是由CommitLog.DefaultAppendMessageCallback执行写入的，DefaultAppendMessageCallback决定了msg在文件中的存储格式：
// CommitLog.DefaultAppendMessageCallback
public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank,
// 数据准备，字段超长则直接返回...
// Determines whether there is sufficient free space
if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) {
// 一. block剩余空间不足，则写入一个特殊的msg，标示已达block末尾
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);
}
// 二、按约定格式写入msg
// 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(bornHostHolder, bornHostLength);
this.msgStoreItemMemory.put(msgInner.getBornHostBytes(bornHostHolder));
// 11 STORETIMESTAMP
this.msgStoreItemMemory.putLong(msgInner.getStoreTimestamp());
// 12 STOREHOSTADDRESS
this.resetByteBuffer(storeHostHolder, storeHostLength);
this.msgStoreItemMemory.put(msgInner.getStoreHostBytes(storeHostHolder));
// 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
byteBuffer.put(this.msgStoreItemMemory.array(), 0, msgLen);
//...
return result;
}数据追加的整体流程如下图
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