High virtual memory consumption on spark-submit client.

[jone]

The virtual memory is 9G When i run org.apache.spark.examples.SparkPi under yarn-cluster model,which using default configurations.
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                        
4519 mqq       20   0 9041m 248m  26m S  0.3  0.8   0:19.85 java 
 I am curious why is so high?

Thanks.