Re: [DISCUSS] KIP-1251: Assignment epochs for consumer groups

[Chia-Ping Tsai]

> You cannot commit partitions that are not assigned to you.

Thanks for the clarification. That sounds good to me, but this new protection 
implies a change to the existing behavior. Therefore, it would be good to 
explicitly mention this in the KIP

For example, the following sendOffsetsToTransaction can succeed today, but will 
fail after this KIP.

  ```java 
 consumer.subscribe(List.of("chia")); 
 ... 
 producer.sendOffsetsToTransaction(Map.of( 
     new TopicPartition("chia", 0), new OffsetAndMetadata(100), 
     new TopicPartition("ikea", 0), new OffsetAndMetadata(100)), // not 
assigned partitions 
     consumer.groupMetadata()); 
 ``` 

Best,
Chia-Ping