Erik Darling looks at exchange spills:
There are quite high waits on PAGEIOLATCH_EX, SLEEP_TASK, and SLEEP_BPOOL_STEAL rounding out the top five. This is quite interesting, because I’ve never explicitly thought of PAGEIOLATCH_EX waits in the context of exchange spills. Normally, I think of them when queries read pages from disk into memory for modification.
Going down the line, SLEEP_TASK is familiar from our time spent with hash spills, but SLEEP_BPOOL_STEAL is so far undocumented anywhere.
Erik also does the math on this query and recommends that you not write a query like this one.