Greg Stark <gsstark(at)mit(dot)edu> writes:
> The run-time of CLUSTER doesn't vary very much based on whether the
> data is already in index order or not. The number of passes only grows
> like log(n) of the size of your data and if you set
> maintenance_work_mem large enough (somewhere around 100MB-1GB) the
> constants are small enough that you're unlikely to even outgrow a
> single pass (plus a final merge though)
Uh ... what? It's not based on the sort code, unless someone rewrote it
since I looked last. It's an index scan and will definitely depend on
the index ordering.
regards, tom lane