[SPARK-10081][Core ] Skip re-computing getMissingParentStages

[viirya]

JIRA: https://issues.apache.org/jira/browse/SPARK-10081

This is a small patch that skips one unnecessary getMissingParentStages calling in handleJobSubmitted.

[SparkQA]

Test build #41105 has finished for PR 8269 at commit 8416b7f.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class ElementwiseProduct(JavaTransformer, HasInputCol, HasOutputCol):

[squito]

lgtm

[SparkQA]

Test build #41509 has finished for PR 8269 at commit 8416b7f.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

Super minor but should this use string interpolation? as a general principle for speed and conciseness, though it won't matter here.

[andrewor14]

How much time does this actually save? This seems fine I wonder if this is actually worth doing since you only traverse the stage hierarchy again, which most likely isn't that deep.

[andrewor14]

On second thought I don't think the optimization here is worth the extra complexity. How much time do you actually save? Even in something like ALS you only have say 20 stages or something. The new signature is actually somewhat confusing: what does it mean to pass in both a stage and its missing stages? What if we accidentally pass in the wrong missing stages?

I would recommend we close this PR since the scheduling delay it saves is negligible.