BewareMyPower commented on issue #11962:
URL: https://github.com/apache/pulsar/issues/11962#issuecomment-915681440


   @codelipenghui The fact is the most existing KoP users prefer 
`entry.format=kafka`. If we changed `entry.format` from `kafka` to `pulsar`, 
all existing topics/data would be not available because the entries are all 
Kafka format.
   - Pulsar consumers cannot recognize these entries without PIP 94.
   - KoP itself cannot recognize these entries because KoP assumes them as 
Pulsar format, so Kafka consumers cannot receive them.
   
   Even without these concerns, you can see following table for the comparison.
   
   | Performance                       | entry.format=kafka | 
entry.format=pulsar |
   | --------------------------------- | ------------------ | 
------------------- |
   | Kafka Producer & Kafka Consumer   | High               | Extremely low     
  |
   | Kafka Producer & Pulsar Consumer  | **Not Available**  | Low               
  |
   | Pulsar Producer & Pulsar Consumer | High               | High              
  |
   | Pulsar Producer & Kafka Consumer  | Low                | Low               
  |
   
   After PIP 94, the **Not Available** entry would become *Low*. The main 
difference is, for all Kafka producers, `entry.format=pulsar` will always 
perform the conversion even if the consumers are also Kafka consumers. 
`entry.format=kafka` performs conversions only if necessary for consumer side.
   
   | Entry's format | Kafka Consumer | Pulsar Consumer |
   | -------------- | -------------- | --------------- |
   | Pulsar         | Conversion     | No conversion   |
   | Kafka          | No conversion  | Conversion      |
   
   After PIP 94, the **No conversion** of first row would become **a check for 
entry buffer**.


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