We didn't provide an unpersist API for Graph because the internal dependency structure of a graph can make it hard to unpersist correctly in a way that avoids recomputation. However, you can directly unpersist a graph's vertices and edges RDDs using graph.vertices.unpersist() and graph.edges.unpersist().
By the way, the memory leak bug with Pregel (SPARK-2025 <https://issues.apache.org/jira/browse/SPARK-2025>) is fixed in master. Ankur <http://www.ankurdave.com/>
