I've somehow missed part of this thread, which is a shame since this is an area of primary concern for me.

Your suggested algorithm seems to be designed to relieve I/O load by making more use of the CPU. (if I followed it correctly). However, that's not PostgreSQL's problem; currently for us external sort is a *CPU-bound* operation, half of which is value comparisons. (oprofiles available if anyone cares)

So we need to look, instead, at algorithms which make better use of work_mem to lower CPU activity, possibly even at the expense of I/O.

--Josh Berkus

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