Pick a smarter Hashed locus for LEFT and RIGHT JOINs.
When determining the locus for a LEFT or RIGHT JOIN, we can use the outer
side's distribution key as is. The EquivalenceClasses from the nullable
side are not of interest above the join, and the outer side's distribution
key can lead to better plans, because it can be made a Hashed locus,
rather than HashedOJ. A Hashed locus can be used for grouping, for
example, unlike a HashedOJ.
This buys back better plans for some INSERT and CTAS queries, that started
to need Redistribute Motions after the previous commit.
Reviewed-by: NMelanie Plageman <mplageman@pivotal.io>
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