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• This proposal ensures backward compatibility by introducing new metrics and modifying existing poll loop and callback mechanisms we do not impact existing Kafka features, APIs, or configurations.

Test Plan

Describe in few sentences how the KIP Metrics will be tested . We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

in org.apache.kafka.connect.mirror.MirrorSourceTaskTest in a unit test fashion. Unfortunately there are no system tests that I could find where this change could be tested, but I am happy to do it if there is a suitable place where it is already done and that I have missed, or to implement a new system test.

Rejected Alternatives

It might be argued that the existing "replication-latency-ms" metric already provides satisfactory information about the replication lag, but I think providing an exact amount of record lagging behind is beneficial in addition to providing a time-lag.

No other alternatives were consideredIf 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.