public static boolean hasRDD(final String name) {
        Spark.refresh();
        return NAME_TO_RDD.containsKey(name);
    }
This is a static cache the prevents Spark from garbage collecting unreferenced RDDs.

@author Marko A. Rodriguez (http://markorodriguez.com)
spark-gremlin/src/main/java/org/apache/tinkerpop/gremlin/spark/structure/Spark.java