View Kafka message headers¶
Apache Kafka (since version 0.11) 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, filtering 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.
Given the actual value is an array of bytes, the developer who produces the messages knows whether this array of bytes represents a string, int, long, double. Lenses can visualize and use the record headers via SQL queries.
To view the headers of messages in Kafka, run:
SELECT HEADERKEYS() as headers FROM trips LIMIT 100
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 here