long lowestActiveOffset() {
        Iterator<BrokerHeartbeatState> iterator = active.iterator();
        if (!iterator.hasNext()) {
            return Long.MAX_VALUE;
        }
        BrokerHeartbeatState first = iterator.next();
        return first.metadataOffset;
    }
Update broker state, including lastContactNs.

@param brokerId          The broker ID.
@param fenced            True only if the broker is currently fenced.
@param metadataOffset    The latest metadata offset of the broker.
@throws IllegalStateException if the broker is not registered.
metadata/src/main/java/org/apache/kafka/controller/BrokerHeartbeatManager.java