13、RocketMQ实战:RocketMQ工作原理之订阅关系的一致性

订阅关系的一致性指的是,同一个消费者组(Group ID相同)下所有Consumer实例所订阅的Topic与Tag及对消息的处理逻辑必须完全一致。
否则,消息消费的逻辑就会混乱,甚至导致消息丢失。

1 正确订阅关系

多个消费者组订阅了多个Topic,并且每个消费者组里的多个消费者实例的订阅关系保持了一致。

2 错误订阅关系

一个消费者组订阅了多个Topic,但是该消费者组里的多个Consumer实例的订阅关系并没有保持一致。

订阅了不同Topic

该例中的错误在于,同一个消费者组中的两个Consumer实例订阅了不同的Topic。
Consumer实例1-1:(订阅了topic为jodie_test_A,tag为所有的消息)

Properties properties = new Properties();
properties.put(PropertyKeyConst.GROUP_ID, "GID_jodie_test_1");
Consumer consumer = ONSFactory.createConsumer(properties);
consumer.subscribe("jodie_test_A", "*", new MessageListener() {
   
     
public Action consume(Message message, ConsumeContext context) {
   
     
System.out.println(message.getMsgID());
return Action.CommitMessage;
}
});

Consumer实例1-2:(订阅了topic为jodie_test_B,tag为所有的消息)

Properties properties = new Properties();
properties.put(PropertyKeyConst.GROUP_ID, "GID_jodie_test_1");
Consumer consumer = ONSFactory.createConsumer(properties);
consumer.subscribe("jodie_test_B", "*", new MessageListener() {
   
     
public Action consume(Message message, ConsumeContext context) {
   
     
System.out.println(message.getMsgID());
return Action.CommitMessage;
}
});

订阅了不同Tag

该例中的错误在于,同一个消费者组中的两个Consumer订阅了相同Topic的不同Tag。
Consumer实例2-1:(订阅了topic为jodie_test_A,tag为TagA的消息)

Properties properties = new Properties();
properties.put(PropertyKeyConst.GROUP_ID, "GID_jodie_test_2");
Consumer consumer = ONSFactory.createConsumer(properties);
consumer.subscribe("jodie_test_A", "TagA", new MessageListener() {
   
     
public Action consume(Message message, ConsumeContext context) {
   
     
System.out.println(message.getMsgID());
return Action.CommitMessage;
}
});

Consumer实例2-2:(订阅了topic为jodie_test_A,tag为所有的消息)

Properties properties = new Properties();
properties.put(PropertyKeyConst.GROUP_ID, "GID_jodie_test_2");
Consumer consumer = ONSFactory.createConsumer(properties);
consumer.subscribe("jodie_test_A", "*", new MessageListener() {
   
     
public Action consume(Message message, ConsumeContext context) {
   
     
System.out.println(message.getMsgID());
return Action.CommitMessage;
}
});

订阅了不同数量的Topic

该例中的错误在于,同一个消费者组中的两个Consumer订阅了不同数量的Topic。
Consumer实例3-1:(该Consumer订阅了两个Topic)

Properties properties = new Properties();
properties.put(PropertyKeyConst.GROUP_ID, "GID_jodie_test_3");
Consumer consumer = ONSFactory.createConsumer(properties);
consumer.subscribe("jodie_test_A", "TagA", new MessageListener() {
   
     
public Action consume(Message message, ConsumeContext context) {
   
     
System.out.println(message.getMsgID());
return Action.CommitMessage;
}
});
consumer.subscribe("jodie_test_B", "TagB", new MessageListener() {
   
     
public Action consume(Message message, ConsumeContext context) {
   
     
System.out.println(message.getMsgID());
return Action.CommitMessage;
}
});

Consumer实例3-2:(该Consumer订阅了一个Topic)

Properties properties = new Properties();
properties.put(PropertyKeyConst.GROUP_ID, "GID_jodie_test_3");
Consumer consumer = ONSFactory.createConsumer(properties);
consumer.subscribe("jodie_test_A", "TagB", new MessageListener() {
   
     
public Action consume(Message message, ConsumeContext context) {
   
     
System.out.println(message.getMsgID());
return Action.CommitMessage;
}
});