一、原理
1、消息存在哪了？
消息持久化的地方其实是磁盘上，在如下目录里的commitlog文件夹里。
/root/store/commitlog
源码如下：
// {@link org.apache.rocketmq.store.config.MessageStoreConfig}
// 数据存储根目录
private String storePathRootDir = System.getProperty("user.home") + File.separator + "store";
// commitlog目录
private String storePathCommitLog = System.getProperty("user.home") + File.separator + "store" + File.separator + "commitlog";
// 每个commitlog文件大小为1GB，超过1GB则创建新的commitlog文件
private int mappedFileSizeCommitLog = 1024 * 1024 * 1024;
比如验证下：
[root@iZ2ze84zygpzjw5bfcmh2hZ commitlog]# pwd
/root/store/commitlog
[root@iZ2ze84zygpzjw5bfcmh2hZ commitlog]# ll -h
total 400K
-rw-r--r-- 1 root root 1.0G Jun 30 18:21 00000000000000000000
[root@iZ2ze84zygpzjw5bfcmh2hZ commitlog]#
可以清晰的看到文件大小是1.0G，超过1.0G再写入消息的话会自动创建新的commitlog文件。
2、关键类解释
2.1、MappedFile
对应的是commitlog文件，比如上面的00000000000000000000文件。
2.2、MappedFileQueue
是MappedFile 所在的文件夹，对 MappedFile 进行封装成文件队列。
2.3、CommitLog
针对 MappedFileQueue 的封装使用。
二、Broker接收消息
1、调用链
BrokerStartup.start() -》 BrokerController.start() -》 NettyRemotingServer.start() -》 NettyRemotingServer.prepareSharableHandlers() -》 new NettyServerHandler() -》 NettyRemotingAbstract.processMessageReceived()
-》 NettyRemotingAbstract.processRequestCommand() -》 SendMessageProcessor.processRequest()
2、processRequest
SendMessageProcessor.processRequest()
@Override
public RemotingCommand processRequest(ChannelHandlerContext ctx,
RemotingCommand request) throws RemotingCommandException {
RemotingCommand response = null;
try {
// 调用asyncProcessRequest
response = asyncProcessRequest(ctx, request).get();
} catch (InterruptedException | ExecutionException e) {
log.error("process SendMessage error, request : " + request.toString(), e);
}
return response;
}
3、asyncProcessRequest
public CompletableFuture<RemotingCommand> asyncProcessRequest(ChannelHandlerContext ctx,
RemotingCommand request) throws RemotingCommandException {
final SendMessageContext mqtraceContext;
switch (request.getCode()) {
// 表示消费者发送的消息，发送者消费失败会重新发回队列进行消息重试
case RequestCode.CONSUMER_SEND_MSG_BACK:
return this.asyncConsumerSendMsgBack(ctx, request);
default:
// 解析header，也就是我们Producer发送过来的消息都在request里，给他解析到SendMessageRequestHeader对象里去。
SendMessageRequestHeader requestHeader = parseRequestHeader(request);
if (requestHeader == null) {
return CompletableFuture.completedFuture(null);
}
mqtraceContext = buildMsgContext(ctx, requestHeader);
// 将解析好的参数放到SendMessageContext对象里
this.executeSendMessageHookBefore(ctx, request, mqtraceContext);
if (requestHeader.isBatch()) {
// 批处理消息用
return this.asyncSendBatchMessage(ctx, request, mqtraceContext, requestHeader);
} else {
// 非批处理，我们这里介绍的核心。
return this.asyncSendMessage(ctx, request, mqtraceContext, requestHeader);
}
}
}
4、asyncSendMessage
private CompletableFuture<RemotingCommand> asyncSendMessage(ChannelHandlerContext ctx, RemotingCommand request,
SendMessageContext mqtraceContext,
SendMessageRequestHeader requestHeader) {
final byte[] body = request.getBody();
int queueIdInt = requestHeader.getQueueId();
TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());
// 拼凑message对象
MessageExtBrokerInner msgInner = new MessageExtBrokerInner();
msgInner.setTopic(requestHeader.getTopic());
msgInner.setQueueId(queueIdInt);
msgInner.setBody(body);
msgInner.setFlag(requestHeader.getFlag());
MessageAccessor.setProperties(msgInner, MessageDecoder.string2messageProperties(requestHeader.getProperties()));
msgInner.setPropertiesString(requestHeader.getProperties());
msgInner.setBornTimestamp(requestHeader.getBornTimestamp());
msgInner.setBornHost(ctx.channel().remoteAddress());
msgInner.setStoreHost(this.getStoreHost());
msgInner.setReconsumeTimes(requestHeader.getReconsumeTimes() == null ? 0 : requestHeader.getReconsumeTimes());
CompletableFuture<PutMessageResult> putMessageResult = null;
Map<String, String> origProps = MessageDecoder.string2messageProperties(requestHeader.getProperties());
// 真正接收消息的方法
putMessageResult = this.brokerController.getMessageStore().asyncPutMessage(msgInner);
return handlePutMessageResultFuture(putMessageResult, response, request, msgInner, responseHeader, mqtraceContext, ctx, queueIdInt);
}
至此我们的消息接收完成了，都封装到了MessageExtBrokerInner对象里。
三、Broker消息存储（持久化）
1、asyncPutMessage
接着上步骤的asyncSendMessage继续看
@Override
public CompletableFuture<PutMessageResult> asyncPutMessage(MessageExtBrokerInner msg) {
CompletableFuture<PutMessageResult> putResultFuture = this.commitLog.asyncPutMessage(msg);
putResultFuture.thenAccept((result) -> {
......
});
return putResultFuture;
}
2、commitLog.asyncPutMessage
public CompletableFuture<PutMessageResult> asyncPutMessage(final MessageExtBrokerInner msg) {
// 获取最后一个文件，MappedFile就是commitlog目录下的那个0000000000文件
MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile();
try {
// 追加数据到commitlog
result = mappedFile.appendMessage(msg, this.appendMessageCallback);
switch (result.getStatus()) {
......
}
// 将内存的数据持久化到磁盘
CompletableFuture<PutMessageStatus> flushResultFuture = submitFlushRequest(result, putMessageResult, msg);
}
}
3、appendMessagesInner
public AppendMessageResult appendMessagesInner(final MessageExt messageExt, final AppendMessageCallback cb) {
// 将消息写到内存
return cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBrokerInner) messageExt);
}
4、doAppend
@Override
public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank,
final MessageExtBrokerInner msgInner) {
// 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;
}
这一步其实就已经把消息保存到缓冲区里了，也就是msgStoreItemMemory，这里采取的NIO。
private final ByteBuffer msgStoreItemMemory;
5、submitFlushRequest
再次回到【2、commitLog.asyncPutMessage】的submitFlushRequest方法，因为之前的方法是将数据已经写到ByteBuffer缓冲区里了，下一步也就是我们现在这一步就要刷盘了。
public CompletableFuture<PutMessageStatus> submitFlushRequest(AppendMessageResult result, PutMessageResult putMessageResult,
MessageExt messageExt) {
// 同步刷盘
if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) {
final GroupCommitService service = (GroupCommitService) this.flushCommitLogService;
if (messageExt.isWaitStoreMsgOK()) {
GroupCommitRequest request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes(),
this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());
service.putRequest(request);
return request.future();
} else {
service.wakeup();
return CompletableFuture.completedFuture(PutMessageStatus.PUT_OK);
}
}
// 异步刷盘
else {
if (!this.defaultMessageStore.getMessageStoreConfig().isTransientStorePoolEnable()) {
flushCommitLogService.wakeup();
} else {
commitLogService.wakeup();
}
return CompletableFuture.completedFuture(PutMessageStatus.PUT_OK);
}
}
6、异步刷盘
class FlushRealTimeService extends FlushCommitLogService {
@Override
public void run() {
while (!this.isStopped()) {
try {
// 每隔500ms刷一次盘
if (flushCommitLogTimed) {
Thread.sleep(500);
} else {
this.waitForRunning(500);
}
// 调用mappedFileQueue的flush方法
CommitLog.this.mappedFileQueue.flush(flushPhysicQueueLeastPages);
} catch (Throwable e) {
}
}
}
}
可看出默认是每隔500毫秒刷一次盘
7、mappedFileQueue.flush
public boolean flush(final int flushLeastPages) {
MappedFile mappedFile = this.findMappedFileByOffset(this.flushedWhere, this.flushedWhere == 0);
if (mappedFile != null) {
// 真正的刷盘操作
int offset = mappedFile.flush(flushLeastPages);
}
}
8、mappedFile.flush
public int flush(final int flushLeastPages) {
if (this.isAbleToFlush(flushLeastPages)) {
try {
if (writeBuffer != null || this.fileChannel.position() != 0) {
// 刷盘 NIO
this.fileChannel.force(false);
} else {
// 刷盘 NIO
this.mappedByteBuffer.force();
}
} catch (Throwable e) {
log.error("Error occurred when force data to disk.", e);
}
}
return this.getFlushedPosition();
}
至此已经全部结束。