Design and Reasons of Publish/Subscribe Model of Message Queue

The model started like this:

Later, in order to be able to deal with the problem of the mismatch between the consumption capacity of consumers and the production capacity of producers.
Problem 1: The production capacity of producers is lower than the consumption capacity of consumers.

         最简单的想法增大生产者生产能力或者减小消费者消费能力。前者不可取，因为消息能生产出来的多少取决于系
         统，取决于业务。而对于上面的模型，P:C=1:1，消费者减无可减，所以也不可取。所以这个问题无解。仔细想
         下，其实一个消费者而已也没有浪费太多性能。

Problem 2: Consumers cannot keep up with the production capacity of producers

       这就引起了下面的设计，一个主题下分成多个队列，原来的一个消费者膨胀成一个消费者组，旗下有多个消费者，
       每个消费者对应一个队列。当需要增大消费能力时，新增队列与消费者组下的消费者即可。

Reprinted by Ao Bing