@Override
    protected void onSerialize(Serializer buf) {
        super.onSerialize(buf);
        buf.putInt(null, path);
        buf.put(null, globalId.getRawId());
        buf.putInt(null, distributionKey);
    }
Returns the distribution key for the node producing this hit.
searchlib/src/main/java/com/yahoo/searchlib/aggregation/FS4Hit.java