Member variable & method

Passing a Member Variable (or) Method of an Object to a Transformation (or) Action results in a complete reference to the object, because of which Spark will transfer the Complete object to the Executors in which it(The Member variable or Method) will be referenced. This results in unnecessary transfer of data(ie.. in order to access one variable/method we end up transferring the entire object). In order to avoid this,always copy the Member variable/method into a local variable before passing it as an argument to the Transformation (or) Action.

class Append(val suffix: String) {

  def appendSuffixBad(inputRDD: RDD[String]): RDD[String] = {
     // Bad      As we are referring the Member variable 'suffix'
     //          the whole object will be serialized & transferred
     //          to the Executor(so that 'suffix' can be referred)
     inputRDD.map { x => x + suffix }             
  }

  def appendSuffixGood(inputRDD: RDD[String]): RDD[String] = {
     // Good      Here we copied the Member variable 'suffix' into a 
     //           local variable, so only the local variable is transferred
     //           to the executor
     val localsuffix = suffix;
     inputRDD.map { x => x + localsuffix }             
  }

}