Futures.md

Future support

A future can be timed as follows:

class Example extends DefaultInstrumented {
  private[this] val loading = metrics.timer("loading")

  def asyncFetchRows(): Future[Seq[Row]] = ???

  def loadStuff(): Future[Seq[Row]] = loading.timeFuture {
    asyncFetchRows()
  }
}

Know what you measure

Method timeFuture does not measure the execution time of the future, instead it measures wall clock time from the moment of calling until the future is completed. If the future was already executed, it will only measure how long it takes to schedule stopping the timer. If the future was not yet executed, it will measure the time it takes to schedule the future for execution in addition to the actual execution.

If you only need to measure the execution time, then use a timer inside the future's execution. For example:

class Example extends DefaultInstrumented {
  private[this] val loading = metrics.timer("loading")

  def fetchRows(): Seq[Row] = ???

  def loadStuff(): Seq[Row] = Future {
    loading.time {
      fetchRows()
    }
  }
}

See the scaladoc for timeFuture in Timer for more gotchas.

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