Heikki Linnakangas <hlinnaka@iki.fi> writes:
> The beauty of the polyphase merge algorithm is that it allows reusing
> input tapes as output tapes efficiently ... So the whole idea of trying to
> efficiently reuse input tapes as output tapes is pointless.
It's been awhile since I looked at that code, but I'm quite certain that
it *never* thought it was dealing with actual tapes. Rather, the point of
sticking with polyphase merge was that it allowed efficient incremental
re-use of temporary disk files, so that the maximum on-disk footprint was
only about equal to the volume of data to be sorted, rather than being a
multiple of that. Have we thrown that property away?
regards, tom lane