RocketMQ消息过滤机制源码详解

#RocketMQ提供了2种消息过滤的方式：

TAG 过滤
SQL92 过滤

SQL过滤默认是没有打开的，如果想要支持，必须在broker的配置文件中设置：enablePropertyFilter = true

一. 示例代码

1.1 producer 代码

public class Producer {

    public static void main(String[] args) throws Exception {

        // 实例化消息生产者Producer

        DefaultMQProducer producer = new DefaultMQProducer("tag_p_g");

        // 设置NameServer的地址

        producer.setNamesrvAddr("127.0.0.1:9876");

        producer.start();

        String[] tags = {"TAG_A", "TAG_B", "TAG_C"};

        for (int i = 0; i < 10 ; i++) {

            byte[] body = ("Hi filter message," + i).getBytes();

            String tag = tags[i % tags.length];

            //同一个topic下，会发送多种tag消息

            Message msg = new Message("MY_topic", tag, body);

            //设置一些属性,消费者SQL过滤时可以使用

            msg.putUserProperty("age", String.valueOf(i));

            msg.putUserProperty("name", "name" + (i + 1));

            msg.putUserProperty("isGender", String.valueOf(new Random().nextBoolean()));

            SendResult sendResult = producer.send(msg);

            System.out.println("sendResult = " + sendResult);

        }

        producer.shutdown();

    }

}

1.2 consumer 代码

1.2.1 TAG过滤

public class Consumer {

    public static void main(String[] args) throws Exception {

        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("c_tag_group");

        consumer.setNamesrvAddr("127.0.0.1:9876");

        /**

         * 订阅消息过滤

         * 只订阅 topic = MY_topic 下

         * tag = TAG_A 或者 tag = TAG_C 的消息,不要 tag = TAG_B 的消息

         * 订阅多个tag使用 || 分开

         */

        consumer.subscribe("MY_topic", "TAG_A || TAG_C");

        consumer.registerMessageListener(new MessageListenerConcurrently() {

            @Override

            public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {

                for (MessageExt msg : msgs) {

                    System.out.println(msg);

                }

                //消费成功时返回

                return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;

            }

        });

        consumer.start();

        System.out.println("Filter Tag Consumer Started");

    }

}

1.2.2 SQL92过滤

public class Consumer {

    public static void main(String[] args) throws Exception {

        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("cg");

        consumer.setNamesrvAddr(MQConstant.NAME_SERVER_ADDR);

        /**

         * 订阅消息过滤: 根据消息生产者指定的用户属性进行过滤

         * 支持的常量类型：

         *   数值：比如：123，3.1415

         *   字符：必须用单引号包裹起来，比如：'abc'

         *   布尔：TRUE 或 FALSE

         *   NULL：特殊的常量，表示空

         *

         * 支持的运算符有：

         *   数值比较：>，>=，<，<=，BETWEEN，=

         *   字符比较：=，<>，IN

         *   逻辑运算 ：AND，OR，NOT

         *   NULL判断：IS NULL 或者 IS NOT NULL

         *

         *   // (age between 6 and 9) AND (name IS NOT NULL) AND (isGender = TRUE)

         */

        consumer.subscribe(MQConstant.FILTER_SQL_TOPIC, MessageSelector.bySql("(age between 6 and 9) AND (name IS NOT NULL) AND (isGender = TRUE)"));

        consumer.registerMessageListener(new MessageListenerConcurrently() {

            @Override

            public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {

                for (MessageExt msg : msgs) {

                    System.out.println(msg);

                }

                //消费成功时返回

                return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;

            }

        });

        consumer.start();

        System.out.println("Filter SQL Consumer Started");

    }

}

二. 说明

消费者去broker拉取消息时，先经过broker过滤一次，在经过消费者过滤一次

如果是 TAG 过滤。broker要先根据ConsumeQueue 中 Tag HashCode过滤一次，消费者在根据 Tag 值过滤一次。因为 ConsumeQueue 为了便于检索，文件中每一个条目都是定长20字节，所以条目在最后八个字节存储的是消息 Tag 的 HashCode，而不是TAG值。这样broker在拉取磁盘中的消息时，只需要对比 ConsumeQueue中的Tag HashCode，而不需要解析 CommitLog 中的 Tag 值，如果发生Hash冲突，则交给消费者客户端过滤消息中的Tag值。
如果是 SQL92 过滤。则全部由 broker 过滤。因为 SQL 过滤的是消息中的属性值，所以必须反序列化 CommitLog 中的属性值，既然在broker已经进行了精确匹配，那么客户端自然可以省去这个步骤了。

三. 消费者启动注册订阅信息到broker

consumer订阅信息会保存到SubscriptionData中，当consumer启动后，会通过心跳先将订阅信息发送到broker。broker主要是构建2部分：

保存consumer发送的订阅信息SubscriptionData对象。
构建SQL过滤的ConsumerFilterData对象。

那么我们看下consumer构建订阅数据以及发送到broker的过程：

// org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl#subscribe(java.lang.String, org.apache.rocketmq.client.consumer.MessageSelector)

public void subscribe(final String topic, final MessageSelector messageSelector) throws MQClientException {

    try {

        if (messageSelector == null) {

            subscribe(topic, SubscriptionData.SUB_ALL);

            return;

        }

        //核心就是创建SubscriptionData

        SubscriptionData subscriptionData = FilterAPI.build(topic,

            messageSelector.getExpression(), messageSelector.getExpressionType());

        this.rebalanceImpl.getSubscriptionInner().put(topic, subscriptionData);

        if (this.mQClientFactory != null) {

            this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();

        }

    } catch (Exception e) {

        throw new MQClientException("subscription exception", e);

    }

}

继续看FilterAPI.build(...)方法：

// org.apache.rocketmq.common.filter.FilterAPI#build

public static SubscriptionData build(final String topic, final String subString,

        final String type) throws Exception {

        // 如果是TAG过滤，则执行这里

        if (ExpressionType.TAG.equals(type) || type == null) {

            return buildSubscriptionData(topic, subString);

        }

        if (subString == null || subString.length() < 1) {

            throw new IllegalArgumentException("Expression can't be null! " + type);

        }

        // 如果是SQL过滤，则执行这里，相对简单，直接原样发送给broker

        SubscriptionData subscriptionData = new SubscriptionData();

        subscriptionData.setTopic(topic);

        subscriptionData.setSubString(subString);

        subscriptionData.setExpressionType(type);

        return subscriptionData;

    }

}

如果是TAG过滤，consumer会做些额外的处理：

// org.apache.rocketmq.common.filter.FilterAPI#buildSubscriptionData

public static SubscriptionData buildSubscriptionData(final String consumerGroup, String topic,

        String subString) throws Exception {

        SubscriptionData subscriptionData = new SubscriptionData();

        subscriptionData.setTopic(topic);

        subscriptionData.setSubString(subString);

        if (null == subString || subString.equals(SubscriptionData.SUB_ALL) || subString.length() == 0) {

            // 订阅所有消息

            subscriptionData.setSubString(SubscriptionData.SUB_ALL);

        } else {

            // 如果订阅的不是*,则通过 || 分割

            String[] tags = subString.split("\\|\\|");

            if (tags.length > 0) {

                for (String tag : tags) {

                    if (tag.length() > 0) {

                        String trimString = tag.trim();

                        if (trimString.length() > 0) {

                            // 保存分割后的TAG值

                            subscriptionData.getTagsSet().add(trimString);

                            // 保存分割后的TAG HashCode

                            subscriptionData.getCodeSet().add(trimString.hashCode());

                        }

                    }

                }

            } else {

                throw new Exception("subString split error");

            }

        }

        return subscriptionData;

    }

这样consumer的订阅信息就准备好了，然后consumer启动，发送心跳数据：

//org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl#start

public synchronized void start() throws MQClientException {

    //......代码省略.......

    // 发送心跳

    this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();

    //......代码省略.......

}

我们再看下broker是如何处理心跳数据的：

public class ClientManageProcessor implements NettyRequestProcessor {

    @Override

    public RemotingCommand processRequest(ChannelHandlerContext ctx, RemotingCommand request)

        throws RemotingCommandException {

        switch (request.getCode()) {

			// 接收客户端心跳指令,保存客户端信息

            case RequestCode.HEART_BEAT:

                return this.heartBeat(ctx, request);

            case RequestCode.UNREGISTER_CLIENT:

                return this.unregisterClient(ctx, request);

            case RequestCode.CHECK_CLIENT_CONFIG:

                return this.checkClientConfig(ctx, request);

            default:

                break;

        }

        return null;

    }

}

heartBeat方法：

// org.apache.rocketmq.broker.processor.ClientManageProcessor#heartBeat

public RemotingCommand heartBeat(ChannelHandlerContext ctx, RemotingCommand request) {

        // 处理消费者心跳

        for (ConsumerData data : heartbeatData.getConsumerDataSet()) {

            SubscriptionGroupConfig subscriptionGroupConfig =

                this.brokerController.getSubscriptionGroupManager().findSubscriptionGroupConfig(

                    data.getGroupName());

            //...

            // 注册消费者信息

            boolean changed = this.brokerController.getConsumerManager().registerConsumer(

                data.getGroupName(),

                clientChannelInfo,

                data.getConsumeType(),

                data.getMessageModel(),

                data.getConsumeFromWhere(),

                data.getSubscriptionDataSet(),

                isNotifyConsumerIdsChangedEnable

            );

            // ...

        }

     	// ...

        return response;

    }

继续往下走：

// org.apache.rocketmq.broker.client.ConsumerManager#registerConsumer

public boolean registerConsumer(final String group, final ClientChannelInfo clientChannelInfo,

    ConsumeType consumeType, MessageModel messageModel, ConsumeFromWhere consumeFromWhere,

    final Set<SubscriptionData> subList, boolean isNotifyConsumerIdsChangedEnable) {

    //...

    // 更新topic下消费组信息

    boolean r2 = consumerGroupInfo.updateSubscription(subList);

    //...

    this.consumerIdsChangeListener.handle(ConsumerGroupEvent.REGISTER, group, subList);

    //...

}

继续往里走：

// org.apache.rocketmq.broker.filter.ConsumerFilterManager#register(java.lang.String, java.lang.String, java.lang.String, java.lang.String, long)

public boolean register(final String topic, final String consumerGroup, final String expression,

    final String type, final long clientVersion) {

    // 如果是TAG 过滤，则退出

    if (ExpressionType.isTagType(type)) {

        return false;

    }

    // 如果是SQL过滤，但没有指定过滤规则，则退出

    if (expression == null || expression.length() == 0) {

        return false;

    }

    FilterDataMapByTopic filterDataMapByTopic = this.filterDataByTopic.get(topic);

    if (filterDataMapByTopic == null) {

        FilterDataMapByTopic temp = new FilterDataMapByTopic(topic);

        FilterDataMapByTopic prev = this.filterDataByTopic.putIfAbsent(topic, temp);

        filterDataMapByTopic = prev != null ? prev : temp;

    }

    BloomFilterData bloomFilterData = bloomFilter.generate(consumerGroup + "#" + topic);

    // 构建SQL过滤的ConsumerFilterData

    return filterDataMapByTopic.register(consumerGroup, expression, type, bloomFilterData, clientVersion);

}

注册方法内部主要就是构建ConsumerFilterData对象：

// org.apache.rocketmq.broker.filter.ConsumerFilterManager#build

public static ConsumerFilterData build(final String topic, final String consumerGroup,

    final String expression, final String type,

    final long clientVersion) {

    if (ExpressionType.isTagType(type)) {

        return null;

    }

    ConsumerFilterData consumerFilterData = new ConsumerFilterData();

    consumerFilterData.setTopic(topic);

    consumerFilterData.setConsumerGroup(consumerGroup);

    consumerFilterData.setBornTime(System.currentTimeMillis());

    consumerFilterData.setDeadTime(0);

    consumerFilterData.setExpression(expression);

    consumerFilterData.setExpressionType(type);

    consumerFilterData.setClientVersion(clientVersion);

    try {

        consumerFilterData.setCompiledExpression(

            FilterFactory.INSTANCE.get(type).compile(expression)

        );

    } catch (Throwable e) {

        log.error("parse error: expr={}, topic={}, group={}, error={}", expression, topic, consumerGroup, e.getMessage());

        return null;

    }

    return consumerFilterData;

}

最终工作的就是：

public class SqlFilter implements FilterSpi {

    @Override

    public Expression compile(final String expr) throws MQFilterException {

        return SelectorParser.parse(expr);

    }

    @Override

    public String ofType() {

        return ExpressionType.SQL92;

    }

}

好了，到这里就铺垫好了，接下来我们继续看消息过滤的过程，这个过程中，上面的2个对象将会工作。

四. 拉取消息

broker处理拉取请求的处理器：PullMessageProcessor 方法内容比较多，还是关注和过滤相关的部分

// org.apache.rocketmq.broker.processor.PullMessageProcessor#processRequest(io.netty.channel.Channel, org.apache.rocketmq.remoting.protocol.RemotingCommand, boolean)

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);

    // .......省略诸多代码........

    SubscriptionData subscriptionData = null;

    ConsumerFilterData consumerFilterData = null;

    // 这里是false, consumer启动时已经将订阅信息发送到了broker，拿来即用即可

    if (hasSubscriptionFlag) {

        try {

            subscriptionData = FilterAPI.build(

                requestHeader.getTopic(), requestHeader.getSubscription(), requestHeader.getExpressionType()

            );

            if (!ExpressionType.isTagType(subscriptionData.getExpressionType())) {

                consumerFilterData = ConsumerFilterManager.build(

                    requestHeader.getTopic(), requestHeader.getConsumerGroup(), requestHeader.getSubscription(),

                    requestHeader.getExpressionType(), requestHeader.getSubVersion()

                );

                assert consumerFilterData != null;

            }

        } catch (Exception e) {

            log.warn("Parse the consumer's subscription[{}] failed, group: {}", requestHeader.getSubscription(),

                requestHeader.getConsumerGroup());

            response.setCode(ResponseCode.SUBSCRIPTION_PARSE_FAILED);

            response.setRemark("parse the consumer's subscription failed");

            return response;

        }

    } else {

        ConsumerGroupInfo consumerGroupInfo =

            this.brokerController.getConsumerManager().getConsumerGroupInfo(requestHeader.getConsumerGroup());

        // ....省略判断.......

        // 获取订阅数据，这个就是consumer启动时发送给broker的

        subscriptionData = consumerGroupInfo.findSubscriptionData(requestHeader.getTopic());

        // .....省略判断.......

        // SQL过滤

        if (!ExpressionType.isTagType(subscriptionData.getExpressionType())) {

            //TODO:前面分析consumer心跳时看到了它，SQL过滤时会创建

            consumerFilterData = this.brokerController.getConsumerFilterManager().get(requestHeader.getTopic(),

                requestHeader.getConsumerGroup());

            // ....省略判断......

        }

    }

    // .....省略判断.......

    MessageFilter messageFilter;

    if (this.brokerController.getBrokerConfig().isFilterSupportRetry()) {

        messageFilter = new ExpressionForRetryMessageFilter(subscriptionData, consumerFilterData,

            this.brokerController.getConsumerFilterManager());

    } else {

        // 创建MessageFilter

        messageFilter = new ExpressionMessageFilter(subscriptionData, consumerFilterData,

            this.brokerController.getConsumerFilterManager());

    }

    // 从broker 拉取消息

    final GetMessageResult getMessageResult =

        this.brokerController.getMessageStore().getMessage(requestHeader.getConsumerGroup(), requestHeader.getTopic(),

            requestHeader.getQueueId(), requestHeader.getQueueOffset(), requestHeader.getMaxMsgNums(), messageFilter);

   //....省略大量代码.....和过滤无关

}

接下来我们就看下从 CommitLog 读取消息并过滤的过程：

// org.apache.rocketmq.store.DefaultMessageStore#getMessage

public GetMessageResult getMessage(final String group, final String topic, final int queueId, final long offset,

    final int maxMsgNums,

    final MessageFilter messageFilter) {

       // .....省略大篇幅代码.......

            // 在去commitlog读取消息之前，对ConsumeQueue条目进行 tag hashcode 过滤

            if (messageFilter != null

                && !messageFilter.isMatchedByConsumeQueue(isTagsCodeLegal ? tagsCode : null, extRet ? cqExtUnit : null)) {

                if (getResult.getBufferTotalSize() == 0) {

                    status = GetMessageStatus.NO_MATCHED_MESSAGE;

                }

                continue;

            }

            // 从CommitLog 读取消息

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

            if (null == selectResult) {

                if (getResult.getBufferTotalSize() == 0) {

                    status = GetMessageStatus.MESSAGE_WAS_REMOVING;

                }

                nextPhyFileStartOffset = this.commitLog.rollNextFile(offsetPy);

                continue;

            }

            // 在从commitlog读取消息之后，进行 SQL 过滤

            if (messageFilter != null

                && !messageFilter.isMatchedByCommitLog(selectResult.getByteBuffer().slice(), null)) {

                if (getResult.getBufferTotalSize() == 0) {

                    status = GetMessageStatus.NO_MATCHED_MESSAGE;

                }

                // release...

                selectResult.release();

                continue;

            }

}

主要就是做3件事：

在去 CommitLog 读取消息之前，先根据 TAG hashcode 过滤一次 ConsumeQueue 中的条目，如果ConsumeQueue中保存Tag HashCode与消费组需要消费Tag HashCode不一致，则不会读取CommitLog中的消息了。

broker先完成tag hashcode 过滤，consumer进一步完成tag 值过滤。

去 CommitLog 读取消息
从 CommitLog 读取出消息之后，如果是SQL过滤，则在broker完成过滤。

4.1 Broker完成 TAG HashCode 过滤

TAG 过滤就是ExpressionMessageFilter#isMatchedByConsumeQueue(..)方法：

@Override

public boolean isMatchedByConsumeQueue(Long tagsCode, ConsumeQueueExt.CqExtUnit cqExtUnit) {

    if (null == subscriptionData) {

        return true;

    }

    if (subscriptionData.isClassFilterMode()) {

        return true;

    }

    // by tags code.

    if (ExpressionType.isTagType(subscriptionData.getExpressionType())) {

        if (tagsCode == null) {

            return true;

        }

        if (subscriptionData.getSubString().equals(SubscriptionData.SUB_ALL)) {

            return true;

        }

        // 根据tag hashcode 过滤

        return subscriptionData.getCodeSet().contains(tagsCode.intValue());

    } else {

       // ....省略else.....

    }

    return true;

}

这个方法内部会完成TAG 的hashcode 过滤，不过这里只是TAG的初步过滤，因为两个不同TAG也可能有相同的hashcode,所以这里过滤并不完善，真正的TAG过滤是交给消费者来完成的。

4.2 Broker完成 SQL 过滤

SQL的过滤是在ExpressionMessageFilter#isMatchedByCommitLog(..)方法中：

@Override

public boolean isMatchedByCommitLog(ByteBuffer msgBuffer, Map<String, String> properties) {

    if (subscriptionData == null) {

        return true;

    }

    if (subscriptionData.isClassFilterMode()) {

        return true;

    }

    // 如果是TAG过滤，则直接退出

    if (ExpressionType.isTagType(subscriptionData.getExpressionType())) {

        return true;

    }

    // SQL过滤的数据（sql表达式等等)

    ConsumerFilterData realFilterData = this.consumerFilterData;

    Map<String, String> tempProperties = properties;

    // .....校验code.....

    Object ret = null;

    try {

        MessageEvaluationContext context = new MessageEvaluationContext(tempProperties);

        ret = realFilterData.getCompiledExpression().evaluate(context);

    } catch (Throwable e) {

        log.error("Message Filter error, " + realFilterData + ", " + tempProperties, e);

    }

    log.debug("Pull eval result: {}, {}, {}", ret, realFilterData, tempProperties);

    if (ret == null || !(ret instanceof Boolean)) {

        return false;

    }

    return (Boolean) ret;

}

这里会根据SQL进行过滤，如果该条消息是消费者想要的，则将其放入容器中，返回给消费者，如果不是消费者想要的，则直接丢弃，继续查询下一条消息。

这里的丢弃只是不返回给消费者，在清除 CommitLog 文件之前，这条消息都是在的。

五. 消费消息

前面说了，如果是TAG 过滤，则Broker会率先完成一次TAG Hashcode过滤，但是这样过滤并不完全，因为不同TAG可能有相同Hashcode,所以消费者要根据TAG 值完成最后的过滤。

如果是SQL过滤，只能由Broker完成，消费者不做其他任何操作。

那么我们还是看消费者消费消息时的过滤逻辑：

// org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl#pullMessage

public void pullMessage(final PullRequest pullRequest) {

    //......

    PullCallback pullCallback = new PullCallback() {

        @Override

        public void onSuccess(PullResult pullResult) {

            if (pullResult != null) {

                // 处理拉取结果，这里将会完成TAG的值过滤

                pullResult = DefaultMQPushConsumerImpl.this.pullAPIWrapper.processPullResult(pullRequest.getMessageQueue(), pullResult,

                    subscriptionData);

            }

        //.......

    }

    //.......

}

那么我们继续看下它的内部实现：

// org.apache.rocketmq.client.impl.consumer.PullAPIWrapper#processPullResult

public PullResult processPullResult(final MessageQueue mq, final PullResult pullResult,

    final SubscriptionData subscriptionData) {

    PullResultExt pullResultExt = (PullResultExt) pullResult;

    this.updatePullFromWhichNode(mq, pullResultExt.getSuggestWhichBrokerId());

    if (PullStatus.FOUND == pullResult.getPullStatus()) {

        ByteBuffer byteBuffer = ByteBuffer.wrap(pullResultExt.getMessageBinary());

        List<MessageExt> msgList = MessageDecoder.decodes(byteBuffer);

        List<MessageExt> msgListFilterAgain = msgList;

        // 根据TAG 值过滤

        if (!subscriptionData.getTagsSet().isEmpty() && !subscriptionData.isClassFilterMode()) {

            msgListFilterAgain = new ArrayList<MessageExt>(msgList.size());

            for (MessageExt msg : msgList) {

                if (msg.getTags() != null) {

                    if (subscriptionData.getTagsSet().contains(msg.getTags())) {

                        msgListFilterAgain.add(msg);

                    }

                }

            }

        }

        // 将过滤后的消息给消费者消费

        pullResultExt.setMsgFoundList(msgListFilterAgain);

        //........

    }

    return pullResult;

}

六. 总结

RocketMQ支持两种方式的消息过滤：TAG/SQL
要想使用SQL过滤，必须要在broker中配置：enablePropertyFilter = true
TAG 过滤分两个阶段完成：

第一阶段：broker率先根据tag的hashcode完成过滤
第二阶段：consumer根据tag值完成最后的过滤

SQL过滤只能在Broker中完成