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TDMQ for Pulsar
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    Message Tag Filtering

    Last updated: 2024-01-03 14:12:49
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      This document describes how to use message tag filtering in TDMQ for Pulsar.

      Feature Description

      A message tag is used to categorize messages under a topic. When a producer in TDMQ for Pulsar sends messages with specified tags, the consumer needs to subscribe to those messages by tag.
      If a consumer configures no tags when subscribing to a topic, all messages in the topic will be delivered to the consumer for consumption.
      Note:
      A single consumer can use multiple tags for a subscription, and the relationship between these tags is OR. Different consumers must use the same tag.

      Use Cases

      Generally, messages with the same business attributes are stored in the same topic. For example, when an order transaction topic contains messages of order placements, payments, and deliveries, and if you want to consume only one type of transaction messages in your business, you can filter them on the client, but this will waste bandwidth resources.
      To solve this problem, TDMQ for Pulsar supports filtering on the broker. You can set one or more tags during message production and subscribe to specified tags during consumption.
      
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      Use Instructions

      Tagged messages are passed in through Properties and can be obtained as follows:
      Java
      Go
      <dependency>
          <groupId>org.apache.pulsar</groupId>
          <artifactId>pulsar-client</artifactId>
          <version>2.10.1</version> <!-- Recommended -->
      </dependency>
      v0.8.0 or later is recommended.
      go get -u github.com/apache/pulsar-client-go@master

      Use Limits of tagged messages

      Tagged messages don't support batch operations. The batch operation feature is enabled by default. To use tagged messages, you need to disable it in the producer as follows:
      Java
      Go
        // Construct a producer
        Producer<byte[]> producer = pulsarClient.newProducer()
                // Disable batch operation
                .enableBatching(false)
                // Complete path of the topic in the format of `persistent://cluster (tenant) ID/namespace/topic name`
                .topic("persistent://pulsar-xxx/sdk_java/topic2").create();
        producer, err := client.CreateProducer(pulsar.ProducerOptions{
            DisableBatching: true, // Disable batch operation
        })
      Tagged message filtering only takes effect for messages with tags; that is, messages without tags won't be filtered and will be pushed to all subscribers instead.
      To enable tagged message, set the Properties field in ProducerMessage when sending messages and set the SubscriptionProperties field in ConsumerOptions when creating consumers.
      When you set the Properties field in ProducerMessage, the key is the tag name, and the value is fixed to TAGS.
      When you set the SubscriptionProperties field in ConsumerOptions, the key is the tag name to be subscribed to, and the value is the tag version, which is reserved for feature extension in the future and has no meaning currently. You can configure as follows:
      Specify one tag
      Java
      Go
       // Send the message
       MessageId msgId = producer.newMessage()
           .property("tag1", "TAGS")
           .value(value.getBytes(StandardCharsets.UTF_8))
              .send();
      
       // Subscription parameters, which can be used to set subscription tags
       HashMap<String, String> subProperties = new HashMap<>();
        subProperties.put("tag1","1");
        // Construct a consumer
        Consumer<byte[]> consumer = pulsarClient.newConsumer()
            // Complete path of the topic in the format of `persistent://cluster (tenant) ID/namespace/topic name`, which can be copied from the **Topic** page.
           .topic("persistent://pulsar-xxxx/sdk_java/topic2")
           // You need to create a subscription on the topic details page in the console and enter the subscription name here
           .subscriptionName("topic_sub1")
           // Declare the shared mode as the consumption mode
           .subscriptionType(SubscriptionType.Shared)
           // Subscription parameters for tag subscription
           .subscriptionProperties(subProperties)
            // Configure consumption starting at the earliest offset; otherwise, historical messages may not be consumed
            .subscriptionInitialPosition(SubscriptionInitialPosition.Earliest).subscribe();
         // Send the message
         if msgId, err := producer.Send(ctx, &pulsar.ProducerMessage{
                    Payload: []byte(fmt.Sprintf("hello-%d", i)),
           Properties: map[string]string{
               "tag1": "TAGS",
           },
         	}); err != nil {
                    log.Fatal(err)
           }
      
      // Create a consumer
           consumer, err := client.Subscribe(pulsar.ConsumerOptions{
                     Topic:            "topic-1",
                     SubscriptionName: "my-sub",
                     SubscriptionProperties: map[string]string{"tag1": "1"},
            })
      Specify multiple tags
      Java
      Go
        // Send the message
          MessageId msgId = producer.newMessage()
              .property("tag1", "TAGS")
              .property("tag2", "TAGS")
            .value(value.getBytes(StandardCharsets.UTF_8))
              .send();
      
       // Subscription parameters, which can be used to set subscription tags
       HashMap<String, String> subProperties = new HashMap<>();
       subProperties.put("tag1","1");
       subProperties.put("tag2","1");
       // Construct a consumer
       Consumer<byte[]> consumer = pulsarClient.newConsumer()
           // Complete path of the topic in the format of `persistent://cluster (tenant) ID/namespace/topic name`, which can be copied from the **Topic** page.
           .topic("persistent://pulsar-xxxx/sdk_java/topic2")
           // You need to create a subscription on the topic details page in the console and enter the subscription name here
           .subscriptionName("topic_sub1")
           // Declare the shared mode as the consumption mode
           .subscriptionType(SubscriptionType.Shared)
           // Subscription parameters for tag subscription
           .subscriptionProperties(subProperties)
           // Configure consumption starting at the earliest offset; otherwise, historical messages may not be consumed
           .subscriptionInitialPosition(SubscriptionInitialPosition.Earliest).subscribe();
        // Create a producer
        if msgId, err := producer.Send(ctx, &pulsar.ProducerMessage{
                   Payload: []byte(fmt.Sprintf("hello-%d", i)),
                     Properties: map[string]string{
                             "tag1": "TAGS",
                             "tag2": "TAGS",
                   },
           }); err != nil {
                   log.Fatal(err)
           }
      
      // Create a consumer
           consumer, err := client.Subscribe(pulsar.ConsumerOptions{
                     Topic:            "topic-1",
                     SubscriptionName: "my-sub",
                     SubscriptionProperties: map[string]string{
                               "tag1": "1",
                               "tag2": "1",
                     },
           })
      Mix tags and properties
      Java
      Go
         // Send the message
         MessageId msgId = producer.newMessage()
             .property("tag1", "TAGS")
             .property("tag2", "TAGS")
             .property("xxx", "yyy")
           .value(value.getBytes(StandardCharsets.UTF_8))
             .send();
      
       // Subscription parameters, which can be used to set subscription tags
       HashMap<String, String> subProperties = new HashMap<>();
       subProperties.put("tag1","1");
       subProperties.put("tag2","1");
       // Construct a consumer
       Consumer<byte[]> consumer = pulsarClient.newConsumer()
           // Complete path of the topic in the format of `persistent://cluster (tenant) ID/namespace/topic name`, which can be copied from the **Topic** page.
           .topic("persistent://pulsar-xxxx/sdk_java/topic2")
           // You need to create a subscription on the topic details page in the console and enter the subscription name here
           .subscriptionName("topic_sub1")
           // Declare the shared mode as the consumption mode
           .subscriptionType(SubscriptionType.Shared)
           // Subscription parameters for tag subscription
           .subscriptionProperties(subProperties)
           // Configure consumption starting at the earliest offset; otherwise, historical messages may not be consumed
           .subscriptionInitialPosition(SubscriptionInitialPosition.Earliest).subscribe();
        // Create a producer
        if msgId, err := producer.Send(ctx, &pulsar.ProducerMessage{
                   Payload: []byte(fmt.Sprintf("hello-%d", i)),
                   Properties: map[string]string{
                             "tag1": "TAGS",
                             "tag2": "TAGS",
                             "xxx": "yyy",
                   },
           }); err != nil {
                   log.Fatal(err)
           }
      
      // Create a consumer
           consumer, err := client.Subscribe(pulsar.ConsumerOptions{
                     Topic:            "topic-1",
                     SubscriptionName: "my-sub",
                     SubscriptionProperties: map[string]string{
                               "tag1": "1",
                               "tag2": "1",
                     },
           })
      Note:
      Once the SubscriptionProperties field is set in the consumer, the tags processed by the subscription cannot be modified. To modify tags, unsubscribe the current subscription first and create a new subscription.
      
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