Unify Sorting Implementations #5879
Description
Is your feature request related to a problem or challenge?
Currently there is separate logic to handle in-memory sorts, spilling sorts, and merging sorts, spread across ExternalSorter, SortPreservingMergeStream. This logic is incredibly hard to follow, and maintain, and there is a high likelihood of inconsistency between the implementations.
Additionally, the in-memory sort implementation currently relies on concatenating batches, which for dictionaries is extremely memory inefficient, as it will concatenate the underlying dictionary values.
Describe the solution you'd like
I would like in-memory sort to proceed by first sorting the batches, and then performing a sort preserving merge
Describe alternatives you've considered
No response
Additional context
This would help with #5230