Consumption mode of Message Oriented Middleware

The consumption pattern of message oriented middleware

Push Pattern ：

advantage The message can be sent to consumers as soon as possible （ stay Pull In this mode, you need to constantly pull messages , Because I don't know whether there are new messages in the message queue ）
Inferiority The server does not know the consumption capacity of the consumer , Constantly sending messages may cause the consumer side buffer to overflow

ActiveMQ Use in prefetch limit Address these weaknesses

 When the number of push messages reaches perfetch limit Specified value , The consumer has not yet returned to the message oriented middleware ACK, Message oriented middleware will no longer push messages to consumers 
 If the number of messages is small ( Producers are producing messages at a slow rate ), But every message   Consumers need a long time to deal with , that prefetch limit Set to 1 More appropriate .
prefetch limit  Set to  0  It means at this time , The consumer polls the message middleware to get the message . No more Push Way , It is Pull Way . That is, consumers take the initiative to pull messages from the message middleware .

Pull Pattern ：

advantage The consumer end can be pulled out according to the processing capacity
Inferiority Will increase message latency （ Consumers don't know when there is news , Can only keep pulling messages , But not too often ; Therefore, a time is usually set , Pull it every once in a while , This time is the message delay time ）

Pull mode

Implementation of various message oriented middleware

• RabbitMQ
  • Consumers default to push mode （ It also supports pull mode ）
• Kafka Pull mode
  • utilize “ Long polling ” To implement pull mode
  • Consumers go to Broker Pull the news , Defines a timeout period , In other words, consumers ask for information , If so, return the message immediately , If not, the consumer waits until the timeout , And then send a pull message request again
• RocketMQ Pull mode
  • RocketMQ Medium PushConsumer In fact, the push mode is actually the pull mode , It just looks like push mode

Long polling

RocketMQ Long polling

Kafka Long polling

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Java Design patterns in source code