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When the barrier batch is encountered during append or during log recovery, all producer entries are removed from the PSM. This ensures leaders, followers, and recovery all handle the barrier consistently. Because the partition is read-only during mirroring, all PSM entries originate from mirrored data. Expiring all entries is safe: no local producer state exists to preserve. Control batches are filtered out by the consumer fetcher via isControlBatch checks. The barrier is invisible to application consumers, just like transaction markers (commit/abort). The log dump tool is enhanced to deserialize and display MIRROR_PID_RESET records.

Chaining

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example

A              B             C
5(A) -------> 5(A) -------> 5(A) # 5(A) means PID:5, source cluster:A
              CB   -------> CB   # Control Batch appended when A failover to B
              5(B) -------> 5(B) # In B and C, even if 2 records with PID 5, they won't duplicate with each other because of the control batch.

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