Since version 0.11, Apache Kafka supports message headers. Headers are a typical concept on messaging systems like JMS and transport systems like TCP or HTTP.
They can be used for routing, filter, and annotation. The header can contain pairs of key=value, where the key is always a string(text), and the value is an array of bytes.
key=value
key
value
Given that the actual value is an array of bytes, the developer who produces the messages knows whether this array of bytes represents a string, an int, a long, or a double. Lenses can visualize and use the record headers via SQL queries.
By deafult lenses fetches the headers of messages and displays them on the UI.
To view the value of a specific header you can run:
SELECT HEADERASSTRING("User") as user FROM trips LIMIT 100
See all available SQL functions
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