protected void handleRecord(ConsumerRecord<byte[], byte[]> record) {
        OffsetSync offsetSync = OffsetSync.deserializeRecord(record);
        TopicPartition sourceTopicPartition = offsetSync.topicPartition();
        offsetSyncs.compute(sourceTopicPartition, (ignored, syncs) ->
                syncs == null ? createInitialSyncs(offsetSync) : updateExistingSyncs(syncs, offsetSync)
        );
    }
Start the OffsetSyncStore, blocking until all previous Offset Syncs have been read from backing storage.
connect/mirror/src/main/java/org/apache/kafka/connect/mirror/OffsetSyncStore.java