[SPARK-1880] [SQL] Eliminate unnecessary job executions.

[ueshin]

There are unnecessary job executions in BroadcastNestedLoopJoin.

When Innner or LeftOuter join, preparation of rightOuterMatches for RightOuter or FullOuter join is not neccessary.
And when RightOuter or FullOuter, it should use not count and then reduce but fold.

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[rxin]

Thanks for submitting this. I actually think this thing is going away to be replaced by broadcast hash join. #734

Maybe we should wait for that to be merged? Otherwise a lot of unnecessary conflicts.

[rxin]

Would be great if you can review that code, @ueshin.

[ueshin]

@rxin Thank you for your comment.
I checked the code #734, not deeply yet, though.
It seems like broadcast hash join is used only for Inner join so broadcast nested loop join will not be replaced.

[rxin]

We can easily add right outer join support to the hash join though. In general, the nested loop join performs very unfavorably compared with a hash join implementation.

[ueshin]

@rxin Ah, you mean that we should add right/full outer join support in addition to #734?
I agree with the unfavorable performance of the nested loop join, so we should wait for being merged and then add the right/full outer join support at another issue.

[ueshin]

@rxin BTW, speaking of performance, could you please review the code #836?
I think this is a kind of blocker issue of join strategy.

[rxin]

Done & merged #836.

[ueshin]

@rxin Thanks a lot!
Well, should I close this PR?

[rxin]

Probably makes sense to close this one now. Thanks!

[ueshin]

Ok, close this. Thanks!