UnsafeExternalSorter

UnsafeExternalSorter is…​FIXME

Creating Instance

UnsafeExternalSorter takes the following to be created:

SerializerManager

UnsafeExternalSorter is given a SerializerManager when created.

UnsafeExternalSorter uses the SerializerManager for getSortedIterator, getIterator, and (SpillableIterator) spill (to request UnsafeSorterSpillWriter for a UnsafeSorterSpillReader).