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3. unclean leader election in cluster A, which causes inconsistent logs

Log truncation in "all replicas"

These cases all have one common root cause: the non-ISRs, which have not completed the log truncation for LMLE, can become the leader (due to unclean leader election), and it breaks the assumption at the beginning of this page:

After log truncation for LMLE, the destination cluster should not contain any record beyond the LMLE.

New topic-level configuration

So, to resolve these cases, we introduce a new "topic-level" config mirror.support.unclean.leader.election . By default it is false. When it is true, during the log truncation for LMLE, we will wait for "all replicas" becomes ISR and completes the log truncation. Again, this is to fulfill the assumption above. So after the log truncation for LMLE, even if there is unclean leader election triggered any time, these log in 2 clusters can still converge successfully using the existing replication protocol.

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