[SPARK-21657][SQL] optimize explode quadratic memory consumpation#19683

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uzadude wants to merge 31 commits intoapache:masterfrom

uzadude:optimize_explode

Commits on Nov 8, 2017

fixed ColumnPruningSuite join plan test
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Commits on Nov 19, 2017

changed indentation
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Commits on Dec 7, 2017

Commits on Dec 22, 2017

Commits on Dec 24, 2017

Commits on Dec 25, 2017

fixing test
uzadude
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Commits on Dec 26, 2017

changed requiredChildOutput to unrequiredChildOutput for easier initialisation in a few places and consolidating all the logic into the Optimizer.
uzadude
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fixed "There should at least one a single empty line separating groups scala and spark"
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