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• FailedPartitionsCount - Count of partitions that have failed. Instead of separate metrics, clientId is used as a tag to distinguish between Replica and ReplicaAlterLogDir fetchers.

• TotalReplicaFetcherThreads - Total replica fetcher threads. (we might add if its useful)

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• The metric FailedPartitionCount would keep track of the failed partitions. It's a newly added metric which would handle partition failure in a better way. It would  avoid losing several healthy partitions in case partition failure occurs.

Rejected Alternatives

• TBDRetries - The thread can make attempts to connect to the failed partition.