RocketMQ 拉取消息-文件获取
看完了上一篇的《RocketMQ 拉取消息-通信模块》，请求进入PullMessageProcessor中，接着
PullMessageProcessor.processRequest(final ChannelHandlerContext ctx, RemotingCommand request)方法中调用了：
final GetMessageResult getMessageResult = this.brokerController.getMessageStore().getMessage(requestHeader.getConsumerGroup(), requestHeader.getTopic(), requestHeader.getQueueId(), requestHeader.getQueueOffset(), requestHeader.getMaxMsgNums(), subscriptionData);
来从硬盘中获取消息体。
接着来看看DefaultMessageStore是如何从消息队列中获取消息的：
/** * 获取消息结果 * 所有的参数都是从requestheader中获取的。也就是说从consumer client端传递过来的。 * @param group * @param topic * @param queueId * @param offset * @param maxMsgNums * @param subscriptionData * @return */ public GetMessageResult getMessage(final String group, final String topic, final int queueId, final long offset, final int maxMsgNums, final SubscriptionData subscriptionData) { if (this.shutdown) { log.warn("message store has shutdown, so getMessage is forbidden"); return null; } if (!this.runningFlags.isReadable()) { log.warn("message store is not readable, so getMessage is forbidden " + this.runningFlags.getFlagBits()); return null; } long beginTime = this.getSystemClock().now(); // 枚举变量，取消息结果 GetMessageStatus status = GetMessageStatus.NO_MESSAGE_IN_QUEUE; // 当被过滤后，返回下一次开始的Offset long nextBeginOffset = offset; // 逻辑队列中的最小Offset long minOffset = 0; // 逻辑队列中的最大Offset long maxOffset = 0; GetMessageResult getResult = new GetMessageResult(); final long maxOffsetPy = this.commitLog.getMaxOffset(); //通过topic和queueid查找逻辑队列对象，相当于字典的目录，用来指定消息在物理文件commitlog上的位置 ConsumeQueue consumeQueue = findConsumeQueue(topic, queueId); if (consumeQueue != null) { minOffset = consumeQueue.getMinOffsetInQuque(); // 消费队列 最小队列编号 maxOffset = consumeQueue.getMaxOffsetInQuque(); // 消费队列 最大队列编号 // 判断 队列位置(offset) if (maxOffset == 0) { // 消费队列无消息 status = GetMessageStatus.NO_MESSAGE_IN_QUEUE; nextBeginOffset = nextOffsetCorrection(offset, 0); } else if (offset < minOffset) { // 查询offset 太小！！！这里可一看出offset的意义 status = GetMessageStatus.OFFSET_TOO_SMALL; nextBeginOffset = nextOffsetCorrection(offset, minOffset); } else if (offset == maxOffset) { // 查询offset 超过 消费队列 一个位置 status = GetMessageStatus.OFFSET_OVERFLOW_ONE; nextBeginOffset = nextOffsetCorrection(offset, offset); } else if (offset > maxOffset) { // 查询offset 超过 消费队列 太多(大于一个位置) status = GetMessageStatus.OFFSET_OVERFLOW_BADLY; if (0 == minOffset) { nextBeginOffset = nextOffsetCorrection(offset, minOffset); } else { nextBeginOffset = nextOffsetCorrection(offset, maxOffset); } } else { // 获得 映射Buffer结果(MappedFile) SelectMapedBufferResult bufferConsumeQueue = consumeQueue.getIndexBuffer(offset); if (bufferConsumeQueue != null) { try { status = GetMessageStatus.NO_MATCHED_MESSAGE; long nextPhyFileStartOffset = Long.MIN_VALUE; // commitLog下一个文件(MappedFile)对应的开始offset。 long maxPhyOffsetPulling = 0; // 消息物理位置拉取到的最大offset int i = 0; final int MaxFilterMessageCount = 16000; final boolean diskFallRecorded = this.messageStoreConfig.isDiskFallRecorded(); // 循环获取 消息位置信息 for (; i < bufferConsumeQueue.getSize() && i < MaxFilterMessageCount; i += ConsumeQueue.CQStoreUnitSize) { long offsetPy = bufferConsumeQueue.getByteBuffer().getLong(); // 消息物理位置offset int sizePy = bufferConsumeQueue.getByteBuffer().getInt(); // 消息长度 long tagsCode = bufferConsumeQueue.getByteBuffer().getLong(); // 消息tagsCode // 设置消息物理位置拉取到的最大offset maxPhyOffsetPulling = offsetPy; // 当 offsetPy 小于 nextPhyFileStartOffset 时，意味着对应的 Message 已经移除，所以直接continue，直到可读取的Message。 if (nextPhyFileStartOffset != Long.MIN_VALUE) { if (offsetPy < nextPhyFileStartOffset) continue; } // 校验 commitLog 是否需要硬盘，无法全部放在内存 boolean isInDisk = checkInDiskByCommitOffset(offsetPy, maxOffsetPy); // 此批消息达到上限了 // 是否已经获得足够消息 if (this.isTheBatchFull(sizePy, maxMsgNums, getResult.getBufferTotalSize(), getResult.getMessageCount(), isInDisk)) { break; } // 消息过滤 // 判断消息是否符合条件 ！！！ if (this.messageFilter.isMessageMatched(subscriptionData, tagsCode)) { // 从commitLog获取对应消息ByteBuffer ！！！ SelectMapedBufferResult selectResult = this.commitLog.getMessage(offsetPy, sizePy);
// 最中从对应的MappedFile对象中通过位置获取到这个数据，下面把它转换为GetMessageResult对象。
if (selectResult != null) { this.storeStatsService.getGetMessageTransferedMsgCount().incrementAndGet(); getResult.addMessage(selectResult); status = GetMessageStatus.FOUND; nextPhyFileStartOffset = Long.MIN_VALUE; } else { // 从commitLog无法读取到消息，说明该消息对应的文件（MappedFile）已经删除，计算下一个MappedFile的起始位置 if (getResult.getBufferTotalSize() == 0) { status = GetMessageStatus.MESSAGE_WAS_REMOVING; } nextPhyFileStartOffset = this.commitLog.rollNextFile(offsetPy); } } else { if (getResult.getBufferTotalSize() == 0) { status = GetMessageStatus.NO_MATCHED_MESSAGE; } if (log.isDebugEnabled()) { log.debug("message type not matched, client: " + subscriptionData + " server: " + tagsCode); } } } // 统计剩余可拉取消息字节数 if (diskFallRecorded) { long fallBehind = maxOffsetPy - maxPhyOffsetPulling; brokerStatsManager.recordDiskFallBehindSize(group, topic, queueId, fallBehind); } // 计算下次拉取消息的消息队列编号 ！！！ nextBeginOffset = offset + (i / ConsumeQueue.CQStoreUnitSize); // 根据剩余可拉取消息字节数与内存判断是否建议读取从节点 long diff = maxOffsetPy - maxPhyOffsetPulling; long memory = (long) (StoreUtil.TotalPhysicalMemorySize * (this.messageStoreConfig.getAccessMessageInMemoryMaxRatio() / 100.0)); getResult.setSuggestPullingFromSlave(diff > memory); } finally { // 必须释放资源 bufferConsumeQueue.release(); } } else { status = GetMessageStatus.OFFSET_FOUND_NULL; nextBeginOffset = nextOffsetCorrection(offset, consumeQueue.rollNextFile(offset)); log.warn("consumer request topic: " + topic + "offset: " + offset + " minOffset: " + minOffset + " maxOffset: " + maxOffset + ", but access logic queue failed."); } } } // 请求的队列Id没有 else { status = GetMessageStatus.NO_MATCHED_LOGIC_QUEUE; nextBeginOffset = nextOffsetCorrection(offset, 0); } // 统计 if (GetMessageStatus.FOUND == status) { this.storeStatsService.getGetMessageTimesTotalFound().incrementAndGet(); } else { this.storeStatsService.getGetMessageTimesTotalMiss().incrementAndGet(); } long eclipseTime = this.getSystemClock().now() - beginTime; this.storeStatsService.setGetMessageEntireTimeMax(eclipseTime); // 设置返回结果 getResult.setStatus(status); getResult.setNextBeginOffset(nextBeginOffset); getResult.setMaxOffset(maxOffset); getResult.setMinOffset(minOffset); return getResult; }
先来看一下获取消息队列的方法：
public ConsumeQueue findConsumeQueue(String topic, int queueId) { ConcurrentHashMap<Integer, ConsumeQueue> map = consumeQueueTable.get(topic); if (null == map) { ConcurrentHashMap<Integer, ConsumeQueue> newMap = new ConcurrentHashMap<Integer, ConsumeQueue>(128); ConcurrentHashMap<Integer, ConsumeQueue> oldMap = consumeQueueTable.putIfAbsent(topic, newMap); if (oldMap != null) { map = oldMap; } else { map = newMap; } } ConsumeQueue logic = map.get(queueId); if (null == logic) { ConsumeQueue newLogic = new ConsumeQueue(// topic, // queueId, // StorePathConfigHelper.getStorePathConsumeQueue(this.messageStoreConfig.getStorePathRootDir()), // this.getMessageStoreConfig().getMapedFileSizeConsumeQueue(), // this); ConsumeQueue oldLogic = map.putIfAbsent(queueId, newLogic); if (oldLogic != null) { logic = oldLogic; } else { logic = newLogic; } } return logic; }
下面看第二个标黄的方法commitlog.getmessage~:
public SelectMapedBufferResult getMessage(final long offset, final int size) { int mapedFileSize = this.defaultMessageStore.getMessageStoreConfig().getMapedFileSizeCommitLog(); MapedFile mapedFile = this.mapedFileQueue.findMapedFileByOffset(offset, (0 == offset ? true : false)); if (mapedFile != null) { int pos = (int) (offset % mapedFileSize); SelectMapedBufferResult result = mapedFile.selectMapedBuffer(pos, size); return result; } return null; }
标黄的方法findMapedFileByOffset：这个方法在《再说rocketmq消息存储》中有介绍。可以到页面上搜关键词找一下。
public MapedFile findMapedFileByOffset(final long offset, final boolean returnFirstOnNotFound) { try { this.readWriteLock.readLock().lock(); MapedFile mapedFile = this.getFirstMapedFile(); if (mapedFile != null) { int index = (int) ((offset / this.mapedFileSize) - (mapedFile.getFileFromOffset() / this.mapedFileSize)); if (index < 0 || index >= this.mapedFiles.size()) { logError .warn( "findMapedFileByOffset offset not matched, request Offset: {}, index: {}, mapedFileSize: {}, mapedFiles count: {}, StackTrace: {}",// offset,// index,// this.mapedFileSize,// this.mapedFiles.size(),// UtilAll.currentStackTrace()); } try { return this.mapedFiles.get(index); } catch (Exception e) { if (returnFirstOnNotFound) { return mapedFile; } } } } catch (Exception e) { log.error("findMapedFileByOffset Exception", e); } finally { this.readWriteLock.readLock().unlock(); } return null; }
MappedFile中获取对应位置的数据。
public SelectMapedBufferResult selectMapedBuffer(int pos, int size) { if ((pos + size) <= this.wrotePostion.get()) { if (this.hold()) { ByteBuffer byteBuffer = this.mappedByteBuffer.slice(); byteBuffer.position(pos); ByteBuffer byteBufferNew = byteBuffer.slice(); byteBufferNew.limit(size); return new SelectMapedBufferResult(this.fileFromOffset + pos, byteBufferNew, size, this); } else { log.warn("matched, but hold failed, request pos: " + pos + ", fileFromOffset: " + this.fileFromOffset); } } else { log.warn("selectMapedBuffer request pos invalid, request pos: " + pos + ", size: " + size + ", fileFromOffset: " + this.fileFromOffset); } return null; }
获取到文件中的消息数据后返回DefaultMessageStore中的方法：
getResult.addMessage(selectResult)
