Frequently Asked Questions

Q: Why do I see messages that say null?

A: If you see null messages then it is because whatever published the message into Kafka published it with a null value (message body).

The most likely reason for this is when using a log compacted topic, that is how you tell Kafka to delete messages with the same message key. This is also referred to as a tombstone.

See Log Compaction in the Kafka documentation for more details. The article Kafka Architecture: Log Compaction also has a good explanation of Kafka log compaction and tombstones.

Q: How many SSE streams can I open in my client application?

You can have as many SSE streams open as you like, even hundreds. They are multiplexed over the same physical HTTP/2 connection, so there isn’t any connection burden when you open more streams.


In violation of the HTTP/2 specification, Google Chrome browser has a built-in restriction that allows up to 256 streams per physical connection. In practice, that means any application which is expected to run in a Google Chrome browser should ensure it doesn’t create more than 256 concurrent open streams.