[SPARK-11039][Documentation][Web UI] Document additional ui configurations

[pnpritchard]

Add documentation for configuration:

• spark.sql.ui.retainedExecutions
• spark.streaming.ui.retainedBatches

[SparkQA]

Test build #43496 has finished for PR 9052 at commit 0ce2f9c.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class ChildProcAppHandle implements SparkAppHandle
  • abstract class LauncherConnection implements Closeable, Runnable
  • final class LauncherProtocol
  • static class Message implements Serializable
  • static class Hello extends Message
  • static class SetAppId extends Message
  • static class SetState extends Message
  • static class Stop extends Message
  • class LauncherServer implements Closeable
  • class NamedThreadFactory implements ThreadFactory
  • class OutputRedirector

[JoshRosen]

LGTM, so I'm going to merge this into master and branch-1.5. Thanks!

[syepes]

@pnpritchard I have just found these settings and they are extremely useful. Do you know is there exits the same options for the Completed Jobs & Stages?
When running a stream jobs for a long time the list gets very big..

Regards,
Sebastian

[syepes]

Sorry for the question I just found these settings:

spark.ui.retainedJobs
spark.ui.retainedStages
spark.worker.ui.retainedExecutors
spark.worker.ui.retainedDrivers

Thanks for this improvement.