dongjinleekr commented on issue #22282: [SPARK-23539][SS] Add support for Kafka 
headers in Structured Streaming
URL: https://github.com/apache/spark/pull/22282#issuecomment-463650960
 
 
   @zsxwing @HeartSaVioR Thank you for the comments. Here are some explanations 
on compatibility issues:
   
   ### 1. About the old brokers (e.g., Kafka 0.10.x broker) which doesn't 
support `headers.`
   
   Kafka's consumer already handles this case: 
https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerRecord.java#L86
 If the given record was forwarded by an old broker without `headers` 
functionality. As @HeartSaVioR pointed out, we are already using 2.1.0 client, 
so we don't have to worry about this.
   
   ### 2. About `KafkaOffsetReader#kafkaSchema` modification
   
   As all of you know, this PR adds the 8th field, `headers,` to 
`KafkaOffsetReader#kafkaSchema.` For continuous reading, it won't be 
problematic - this field will be ignored with the old SQL queries. In my 
opinion, the same holds for continuous writing. Older writing queries without 
the `headers` column will not conflict with the update, and the queries with 
`headers` can't be valid.
   
   +1.
   
   > I wonder if there has been some cases on datasource option to be allowed 
to affect schema. (by @HeartSaVioR)
   
   As far as I know, there is no datasource option which affects the schema.

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