Raised the default for orderby threads from 4 to 16.
Removed if LIMIT check block in makeVtableModeSteps().
Removed a duplicate of TimeCompare class and methods.
MCOL-3536 Upmerged the change.
MCOL-894 Post review changes.
Uncomment if LIMIT check block in makeVtableModeSteps().
TupleAnnexStep dtor now uses vector::size() as a boundary.
Removed useless try-catch blocks.
executeParallelOrderBy() now calculates rowSize only once.
Removed forward declaration in the unexisting namespace.
Trim UTs a bit.
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