Difference in key/value subjects in Schema Registry

Question

I'm a newbie in schema registry in Kafka, but I cannot realize what's the difference between kafka-value and kafka-key in schema registry? I registered a new topic: test Now, if I make a request to /subjects I have:

• test
• test-value So my question:

1. what the difference between them? If I wanted to update schema I have to update key or value?
2. why I need key with schema and different versions and value with a different version?
3. why in control center key for shcema is empty?

Answer 1

Kafka message can have headers, key, payload... the key 🔑 and the payload (value) can have schemas, they are maintained in different "subject" the topic-key is for schemas for the key, the topic-value is for the schemas of the payload