@Override
    public String toString() {
        return String.format("Partition(topic = %s, partition = %d, leader = %s, replicas = %s, isr = %s, offlineReplicas = %s)",
                             topic,
                             partition,
                             leader == null ? "none" : leader.idString(),
                             formatNodeIds(replicas),
                             formatNodeIds(inSyncReplicas),
                             formatNodeIds(offlineReplicas));
    }
The subset of the replicas that are offline
clients/src/main/java/org/apache/kafka/common/PartitionInfo.java