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The controller thread is responsible for critical cluster coordination tasks, including leadership elections, topic metadata updates, partition assignments, and Raft-based state changes. However, there is currently no metric to measure how much time the controller spends actively processing work versus waiting for new events or Raft callbacks. This lack of visibility makes it challenging to assess the controller’s performance, detect potential bottlenecks, or optimize resource allocation in high-load scenarios. This KIP proposes introducing a new metric to monitor the controller thread’s idleness ratio.

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Compatibility, Deprecation, and Migration Plan

We adds one new metric so there will be no behaviour changes and This KIP introduces a single new metric, with no changes to existing behavior, APIs, or protocols. There will be no impact on existing kafka Kafka versions.

Test Plan

We will add unit test tests to verify the correctness of the metric. 

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.