RocketMQ中broker消息存儲之如何添加消息

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broker存儲子系統追加消息的入口是DefaultMessageStore.asyncPutMessage，該方法會調用CommitLog.asyncPutMessage，主要實現如下：

    // CommitLog.java
    public CompletableFuture<PutMessageResult> asyncPutMessage(final MessageExtBrokerInner msg) {
        // msg準備...

        // 1. 獲取最后一個block，準備寫入
        MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile();

        putMessageLock.lock(); //spin or ReentrantLock ,depending on store config
        try {
            //....

            if (null == mappedFile || mappedFile.isFull()) { // 加鎖后重試一次，嘗試新建一個block
                mappedFile = this.mappedFileQueue.getLastMappedFile(0); // Mark: NewFile may be cause noise
            }
            if (null == mappedFile) { // 新建block失敗，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剩余空間不足，新建下一個block，再次嘗試寫入
                    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;
                // 發送錯誤，失敗返回...
            }

            // ...
        } finally {
            putMessageLock.unlock();
        }

        // 4. 提交刷盤請求
        CompletableFuture<PutMessageStatus> flushResultFuture = submitFlushRequest(result, putMessageResult, msg);
        // 5. 提交同步請求
        CompletableFuture<PutMessageStatus> 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在執行數據追加時實際調用的是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;
            // 調用callback執行實際的數據寫入，callback實現決定了數據的存儲格式
            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實際是由CommitLog.DefaultAppendMessageCallback執行寫入的，DefaultAppendMessageCallback決定了msg在文件中的存儲格式：

        // CommitLog.DefaultAppendMessageCallback
        public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank,
            // 數據準備，字段超長則直接返回...

            // Determines whether there is sufficient free space
            if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) {
                // 一. block剩余空間不足，則寫入一個特殊的msg，標示已達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、按約定格式寫入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;
        }

數據追加的整體流程如下圖

以上是“RocketMQ中broker消息存儲之如何添加消息”這篇文章的所有內容，感謝各位的閱讀！相信大家都有了一定的了解，希望分享的內容對大家有所幫助，如果還想學習更多知識，歡迎關注億速云行業資訊頻道！