Commit 8b304b8b removed replacement
selection, but left behind this comment text.  The optimization to
which the comment refers is not relevant without replacement
selection, because if we had so few tuples as to require only one
tape, we would have just completed the sort in memory.

Peter Geoghegan

Discussion: http://postgr.es/m/CAH2-WznqupLA8CMjp+vqzoe0yXu0DYYbQSNZxmgN76tLnAOZ_w@mail.gmail.com