SortPreservingMerge does not account for memory usage #5885
Description
Is your feature request related to a problem or challenge?
SortPreservingMerge currently has extremely limited memory accounting functionality, with no accounting for buffered batches or cursors.
The only memory accounting is a static assignment at construction time by ExternalSorter of the size of the in memory batches, when merging spilled and in-memory data. This assignment is never decremented, and does not take into account any memory usage resulting from loading the spilled data back into memory.
Describe the solution you'd like
SortPreservingMerge should account for the memory usage of the data it has buffered
Additionally the various streams created by ExternalSorter, both for in-memory and spilled data, should be accounted for
Describe alternatives you've considered
No response
Additional context
#5879 tracks unifying the sorting implementations, which may help make this story more consistent.