BewareMyPower commented on issue #15704:
URL: https://github.com/apache/pulsar/issues/15704#issuecomment-1133917552

   I think it's a common problem for clients of all languages. This check was 
introduced in https://github.com/apache/pulsar/pull/1103.
   
   ```java
       MultiTopicsConsumerImpl(/* ... */) {
           super(client, singleTopic, conf, Math.max(2, 
conf.getReceiverQueueSize()), executorProvider, subscribeFuture,
                   schema, interceptors);
   
           checkArgument(conf.getReceiverQueueSize() > 0,
               "Receiver queue size needs to be greater than 0 for Topics 
Consumer");
   ```
   
   IMO, it's a bug. It looks like the multi topics consumer requires the 
receiver queue size is at least 2. (from the `Math.max(2, 
conf.getReceiverQueueSize())` call). I guess in the early time of Pulsar, the 
number of partitions must be at least 2, so we have this check.
   
   But the zero queue consumer should be an exceptional case. We should fix 
both Java and C++ clients for this config. @codelipenghui 


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