BewareMyPower commented on issue #11962:
URL: https://github.com/apache/pulsar/issues/11962#issuecomment-915738177


   @codelipenghui The default `entry.format` is `pulsar` is just because 
there's no way to interact among Pulsar clients and Kafka clients when 
`entry.format` is `kafka` before. https://github.com/streamnative/kop/pull/632 
fixed a part of this problem so that Kafka consumer can consume messages from 
Pulsar producer. But if we want Pulsar consumer to consume messages from Kafka 
producer, we need to fix the broker side. If we have the PIP 94, things became 
easy. `entry.format=pulsar` would be deprecated. Regarding to the case there're 
multiple subscriptions on the same topic, it's just a **bad vs more bad** 
compare.
   
   > after we increase the burden of the broker, will this meet the user's 
performance requirements?
   
   It's still a priority comparison I've said before: **availability vs. 
performance**. We should tell user **not to use older Pulsar clients.** I 
accept both cases, just need to change PIP 94 to `Message converter at client 
level`, we still have the converter but it should only be added to client's 
config.
   
   > If users set up incorrect format before, they should do the topic 
migration before we provided the solution.
   
   It's nearly impossible. The `entry.format` config is broker level. For 
example, if you have N messages with `entry.format=pulsar`, you can read them 
all with Pulsar consumer and **persist them somewhere**. Then change the 
`entry.format` to `kafka`, restart the broker, and **retrieve messages from 
somewhere and publish them to new topics**. Changing `entry.format` from 
`kafka` to `pulsar` is the same.


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