What do the numbers on the progress bar mean in spark-shell?

Question

In my spark-shell, what do entries like the below mean when I execute a function ?

[Stage7:===========>                              (14174 + 5) / 62500         


        

Answer 1

What you get is a Console Progress Bar, [Stage 7: shows the stage you are in now, and (14174 + 5) / 62500] is (numCompletedTasks + numActiveTasks) / totalNumOfTasksInThisStage]. The progress bar shows numCompletedTasks / totalNumOfTasksInThisStage.

It will be shown when both spark.ui.showConsoleProgress is true (by default) and log level in conf/log4j.properties is ERROR or WARN (!log.isInfoEnabled is true).

Let's see the code in ConsoleProgressBar.scala that shows it out:

private def show(now: Long, stages: Seq[SparkStageInfo]) {
  val width = TerminalWidth / stages.size
  val bar = stages.map { s =>
    val total = s.numTasks()
    val header = s"[Stage ${s.stageId()}:"
    val tailer = s"(${s.numCompletedTasks()} + ${s.numActiveTasks()}) / $total]"
    val w = width - header.length - tailer.length
    val bar = if (w > 0) {
      val percent = w * s.numCompletedTasks() / total
      (0 until w).map { i =>
        if (i < percent) "=" else if (i == percent) ">" else " "
      }.mkString("")
    } else {
    ""
    }
    header + bar + tailer
  }.mkString("")

  // only refresh if it's changed of after 1 minute (or the ssh connection will be closed
  // after idle some time)
  if (bar != lastProgressBar || now - lastUpdateTime > 60 * 1000L) {
    System.err.print(CR + bar)
    lastUpdateTime = now
  }
  lastProgressBar = bar
}

Answer 2

Let's assume you see the following (X,A,B,C are always non negative integers):

[Stage X:==========>            (A + B) / C]

(for example in the question X=7, A=14174, B=5 and C=62500)

Here is what is going on at a high level: Spark breaks the work in stages and tasks in each stage. This progress indicator means that Stage X is comprised of C tasks. During the execution, A and B start at zero and keep changing. A is always the number of tasks already finished and B is the number of tasks currently executing. For a stage with many tasks (way more than the workers you have) you should expect to see B grow to a number that corresponds to how many workers you have in the cluster, then you should start seeing A increase as tasks complete. Towards the end, as the last few tasks execute, B will start decreasing until it reaches 0, at which point A should equal C, the stage is done, and spark moves to the next stage. C will stay constant during the whole time, remember it is the total number of tasks in the stage and never changes.

The ====> shows the percentage of work done based on what I described above. At the beginning the > will be towards the left and will be moving to the right as tasks are completed.