Modifying the SparkR sources to use a specified engine

The SparkR package we tested assumes that worker nodes can call the R engine using the hard-wired command Rscript. To use SparkR with TIBCO Enterprise Runtime for R (TERR), we needed to change SparkR sources so it can call a different engine instead.

• Change the SparkR source code to allow a different command to invoke the engine by making the following change to the file SparkR-pkg/pkg/src/src/main/ scala/edu/berkeley/cs/amplab/ sparkr/RRDD.scala.
  Change

   private def createRProcess(rLibDir: String, port: Int, script: String) = {
      val rCommand = "Rscript"
      val rOptions = "--vanilla"
  ...

  to

  private def createRProcess(rLibDir: String, port: Int, script: String) = {
      val rCommand = SparkEnv.get.conf.get("spark.sparkr.r.command",
                                           "Rscript")
      val rOptions = "--vanilla"
      ...

  Note: At some point, we hope that we can contribute this change to the SparkR sources.