public long offsetLag() {
        return offsetLag;
    }
The lag of the log's LEO with respect to the partition's
high watermark (if it is the current log for the partition)
or the current replica's LEO (if it is the {@linkplain #isFuture() future log}
for the partition).
clients/src/main/java/org/apache/kafka/clients/admin/ReplicaInfo.java