Rocketmq消息持久化

本文编写，参考：https://my.oschina.net/bieber/blog/725646

producer Send()的Message最终将由broker处理，处理类为：SendMessageProcessor ,处理方法：processRequet.

public class SendMessageProcessor extends AbstractSendMessageProcessor implements NettyRequestProcessor {

    private List<ConsumeMessageHook> consumeMessageHookList;

    public SendMessageProcessor(final BrokerController brokerController) {
        super(brokerController);
    }

    @Override
    public RemotingCommand processRequest(ChannelHandlerContext ctx, RemotingCommand request) throws RemotingCommandException {}
上述方法，并不是直接处理消息，而是交由MessageStore处理，相关代码如下：

MessageExtBrokerInner msgInner = new MessageExtBrokerInner();
msgInner.setTopic(requestHeader.getTopic());
msgInner.setQueueId(queueIdInt);
//......
PutMessageResult putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);

然而MessageStore也不直接持久化消息，转交给 CommitLog

long beginTime = this.getSystemClock().now();
PutMessageResult result = this.commitLog.putMessages(messageExtBatch);

从MappedFileQueue中取出最新的一条：

MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile();
 //写消息

result = mappedFile.appendMessages(messageExtBatch, this.appendMessageCallback);
  //持久化到磁盘,最终通过FileChannel持久化到文件
handleDiskFlush(result, putMessageResult, messageExtBatch);

handleHA(result, putMessageResult, messageExtBatch);


2.cousumer 从broker读消息。
消费者从broker读取消息经由PullMessageProcessor类处理的，processRequest()方法处理请求：

RemotingCommand processRequest(final Channel channel, RemotingCommand request, boolean brokerAllowSuspend)

经过一系列的判断处理，之后交由 MessageStore：

final GetMessageResult getMessageResult =
    this.brokerController.getMessageStore().getMessage(requestHeader.getConsumerGroup(), requestHeader.getTopic(),
        requestHeader.getQueueId(), requestHeader.getQueueOffset(), requestHeader.getMaxMsgNums(), messageFilter);
读取消息。
之后交由commitLog，读出消息，

SelectMappedBufferResult selectResult = this.commitLog.getMessage(offsetPy, sizePy);

可以看到是先从ConsumerQueue中获取消息索引，然后再从commitlog中读取消息内容。这些内容也是在存储消息的时候写入的。

相关也可参考：http://jm.taobao.org/2017/01/12/rocketmq-quick-start-in-10-minutes/