Message consumption error: UnknownGroup (Local: Unknown group)

[maingoh]

Describe the bug

When bumping from 2.8.2 to 2.8.3 I am periodically seeing this message for all the kafka sources. They seem to work, but the log seem suspicious. Is everything fine ?

Error message/log

risingwave-meta-0 meta 2026-05-14T22:57:03.149096327Z  WARN risingwave_connector::source::kafka::enumerator: failed to poll kafka client error=Message consumption error: UnknownGroup (Local: Unknown group) topic="foo" broker_address="redpanda.com:9092"

To Reproduce

No response

Expected behavior

No response

How did you deploy RisingWave?

Kubernetes operator

The version of RisingWave

2.8.3

Additional context

No response

[hzxa21]

@tabVersion Do you know?

[tabVersion]

Thanks for reporting this!

I checked the code path, and this looks like a misleading warning introduced in v2.8.3, not a real Kafka source consumption failure.
The related change is #25411, which cherry-picked #25405 into release-2.8. That change added a non-blocking poll(Duration::ZERO) in the meta-side Kafka split enumerator. This enumerator is used by meta for
split discovery / metadata / watermark fetching, and it does not configure a Kafka group.id.

The actual compute-side Kafka source reader, which consumes records, does configure group.id.

Because the meta-side enumerator has no consumer group, librdkafka can return UnknownGroup (Local: Unknown group) when the new poll path is called. RisingWave then logs that as:

failed to poll kafka client error=Message consumption error: UnknownGroup (Local: Unknown group)

So if the sources are otherwise consuming normally, this warning should not indicate data loss or a stopped Kafka source reader. It is from the meta split-discovery path.

However, the warning is confusing and should probably be fixed/downgraded/suppressed for this expected no-group enumerator case. We will fix it.