RocketMQ设计之主从复制和读写分离

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brokerClusterName = DefaultCluster
brokerName = broker-a
brokerId = 0
deleteWhen = 04
fileReservedTime = 48
brokerRole = ASYNC_MASTER
flushDiskType = ASYNC_FLUSH

public class GetMessageResult {

    private final List<SelectMappedBufferResult> messageMapedList =
        new ArrayList<SelectMappedBufferResult>(100);
    private final List<ByteBuffer> messageBufferList = new ArrayList<ByteBuffer>(100);
    private GetMessageStatus status;
    private long nextBeginOffset;
    private long minOffset;
    private long maxOffset;
    private int bufferTotalSize = 0;
    // 标识是否通过Slave拉拉取消息
    private boolean suggestPullingFromSlave = false;
    private int msgCount4Commercial = 0;
}

// 针对消息堆积量过大会切换到Slave进行查询。
// maxOffsetPy 为当前最大物理偏移量，maxPhyOffsetPulling 为本次消息拉取最大物理偏移量，他们的差即可表示消息堆积量。
// TOTAL_PHYSICAL_MEMORY_SIZE 表示当前系统物理内存，accessMessageInMemoryMaxRatio 的默认值为 40，
// 以上逻辑即可算出当前消息堆积量是否大于物理内存的 40%，如果大于则将 suggestPullingFromSlave 设置为 true。

long diff = maxOffsetPy - maxPhyOffsetPulling;
long memory = (long) (StoreUtil.TOTAL_PHYSICAL_MEMORY_SIZE
    * (this.messageStoreConfig.getAccessMessageInMemoryMaxRatio() / 100.0));
getResult.setSuggestPullingFromSlave(diff > memory);

public class PullMessageResponseHeader implements CommandCustomHeader {
    // suggestWhichBrokerId标识从哪个broker进行查询
    private Long suggestWhichBrokerId;
    private Long nextBeginOffset;
    private Long minOffset;
    private Long maxOffset;
}


public class PullMessageProcessor implements NettyRequestProcessor {

    private RemotingCommand processRequest(final Channel channel, RemotingCommand request, boolean brokerAllowSuspend)
        throws RemotingCommandException {
        RemotingCommand response = RemotingCommand.createResponseCommand(PullMessageResponseHeader.class);
        final PullMessageResponseHeader responseHeader = (PullMessageResponseHeader) response.readCustomHeader();
        final PullMessageRequestHeader requestHeader =
            (PullMessageRequestHeader) request.decodeCommandCustomHeader(PullMessageRequestHeader.class);

        response.setOpaque(request.getOpaque());

        final GetMessageResult getMessageResult =
            this.brokerController.getMessageStore().getMessage(requestHeader.getConsumerGroup(), requestHeader.getTopic(),
                requestHeader.getQueueId(), requestHeader.getQueueOffset(), requestHeader.getMaxMsgNums(), messageFilter);

        if (getMessageResult != null) {
            response.setRemark(getMessageResult.getStatus().name());
            responseHeader.setNextBeginOffset(getMessageResult.getNextBeginOffset());
            responseHeader.setMinOffset(getMessageResult.getMinOffset());
            responseHeader.setMaxOffset(getMessageResult.getMaxOffset());

            // 建议从slave消费消息
            if (getMessageResult.isSuggestPullingFromSlave()) {
                // 从slave查询
                responseHeader.setSuggestWhichBrokerId(subscriptionGroupConfig.getWhichBrokerWhenConsumeSlowly());
            } else {
                // 从master查询
                responseHeader.setSuggestWhichBrokerId(MixAll.MASTER_ID);
            }

            switch (this.brokerController.getMessageStoreConfig().getBrokerRole()) {
                case ASYNC_MASTER:
                case SYNC_MASTER:
                    break;
                case SLAVE:
                    // 针对SLAVE需要判断是否可读，不可读的情况下读MASTER
                    if (!this.brokerController.getBrokerConfig().isSlaveReadEnable()) {
                        response.setCode(ResponseCode.PULL_RETRY_IMMEDIATELY);
                        responseHeader.setSuggestWhichBrokerId(MixAll.MASTER_ID);
                    }
                    break;
            }

            if (this.brokerController.getBrokerConfig().isSlaveReadEnable()) {
                // consume too slow ,redirect to another machine
                if (getMessageResult.isSuggestPullingFromSlave()) {
                    responseHeader.setSuggestWhichBrokerId(subscriptionGroupConfig.getWhichBrokerWhenConsumeSlowly());
                }
                // consume ok
                else {
                    responseHeader.setSuggestWhichBrokerId(subscriptionGroupConfig.getBrokerId());
                }
            } else {
                responseHeader.setSuggestWhichBrokerId(MixAll.MASTER_ID);
            }
        }

        return response;
    }
}

public class PullAPIWrapper {
    private final InternalLogger log = ClientLogger.getLog();
    private final MQClientInstance mQClientFactory;
    private final String consumerGroup;
    private final boolean unitMode;
    private ConcurrentMap<MessageQueue, AtomicLong/* brokerId */> pullFromWhichNodeTable =
        new ConcurrentHashMap<MessageQueue, AtomicLong>(32);
    private volatile boolean connectBrokerByUser = false;
    private volatile long defaultBrokerId = MixAll.MASTER_ID;
    private Random random = new Random(System.currentTimeMillis());
    private ArrayList<FilterMessageHook> filterMessageHookList = new ArrayList<FilterMessageHook>();

    public PullResult processPullResult(final MessageQueue mq, final PullResult pullResult,
        final SubscriptionData subscriptionData) {
        PullResultExt pullResultExt = (PullResultExt) pullResult;

        // 处理MessageQueue对应拉取的brokerId
        this.updatePullFromWhichNode(mq, pullResultExt.getSuggestWhichBrokerId());

        // 省略相关代码

        pullResultExt.setMessageBinary(null);

        return pullResult;
    }

    public void updatePullFromWhichNode(final MessageQueue mq, final long brokerId) {
        // 保存在pullFromWhichNodeTable对象中
        AtomicLong suggest = this.pullFromWhichNodeTable.get(mq);
        if (null == suggest) {
            this.pullFromWhichNodeTable.put(mq, new AtomicLong(brokerId));
        } else {
            suggest.set(brokerId);
        }
    }
}

public class PullAPIWrapper {
    private final InternalLogger log = ClientLogger.getLog();
    private final MQClientInstance mQClientFactory;
    private final String consumerGroup;
    private final boolean unitMode;
    private ConcurrentMap<MessageQueue, AtomicLong/* brokerId */> pullFromWhichNodeTable =
        new ConcurrentHashMap<MessageQueue, AtomicLong>(32);
    private volatile boolean connectBrokerByUser = false;
    private volatile long defaultBrokerId = MixAll.MASTER_ID;
    private Random random = new Random(System.currentTimeMillis());
    private ArrayList<FilterMessageHook> filterMessageHookList = new ArrayList<FilterMessageHook>();

    public PullResult pullKernelImpl(
        final MessageQueue mq,
        final String subExpression,
        final String expressionType,
        final long subVersion,
        final long offset,
        final int maxNums,
        final int sysFlag,
        final long commitOffset,
        final long brokerSuspendMaxTimeMillis,
        final long timeoutMillis,
        final CommunicationMode communicationMode,
        final PullCallback pullCallback
    ) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {

        // 查找MessageQueue应该从brokerName的哪个节点查询
        FindBrokerResult findBrokerResult =
            this.mQClientFactory.findBrokerAddressInSubscribe(mq.getBrokerName(),
                this.recalculatePullFromWhichNode(mq), false);

        if (null == findBrokerResult) {
            this.mQClientFactory.updateTopicRouteInfoFromNameServer(mq.getTopic());
            findBrokerResult =
                this.mQClientFactory.findBrokerAddressInSubscribe(mq.getBrokerName(),
                    this.recalculatePullFromWhichNode(mq), false);
        }

        if (findBrokerResult != null) {
            {
                // check version
                if (!ExpressionType.isTagType(expressionType)
                    && findBrokerResult.getBrokerVersion() < MQVersion.Version.V4_1_0_SNAPSHOT.ordinal()) {
                    throw new MQClientException("The broker[" + mq.getBrokerName() + ", "
                        + findBrokerResult.getBrokerVersion() + "] does not upgrade to support for filter message by " + expressionType, null);
                }
            }
            int sysFlagInner = sysFlag;

            if (findBrokerResult.isSlave()) {
                sysFlagInner = PullSysFlag.clearCommitOffsetFlag(sysFlagInner);
            }

            PullMessageRequestHeader requestHeader = new PullMessageRequestHeader();
            requestHeader.setConsumerGroup(this.consumerGroup);
            requestHeader.setTopic(mq.getTopic());
            requestHeader.setQueueId(mq.getQueueId());
            requestHeader.setQueueOffset(offset);
            requestHeader.setMaxMsgNums(maxNums);
            requestHeader.setSysFlag(sysFlagInner);
            requestHeader.setCommitOffset(commitOffset);
            requestHeader.setSuspendTimeoutMillis(brokerSuspendMaxTimeMillis);
            requestHeader.setSubscription(subExpression);
            requestHeader.setSubVersion(subVersion);
            requestHeader.setExpressionType(expressionType);

            String brokerAddr = findBrokerResult.getBrokerAddr();
            if (PullSysFlag.hasClassFilterFlag(sysFlagInner)) {
                brokerAddr = computPullFromWhichFilterServer(mq.getTopic(), brokerAddr);
            }

            PullResult pullResult = this.mQClientFactory.getMQClientAPIImpl().pullMessage(
                brokerAddr,
                requestHeader,
                timeoutMillis,
                communicationMode,
                pullCallback);

            return pullResult;
        }

        throw new MQClientException("The broker[" + mq.getBrokerName() + "] not exist", null);
    }


    public long recalculatePullFromWhichNode(final MessageQueue mq) {
        if (this.isConnectBrokerByUser()) {
            return this.defaultBrokerId;
        }

        AtomicLong suggest = this.pullFromWhichNodeTable.get(mq);
        if (suggest != null) {
            return suggest.get();
        }

        return MixAll.MASTER_ID;
    }
}