Browse the archives again!  That option was never documented and has since been
dropped for several reasons:  It does not work safely!  You risk your data if
you use it.  This was covered on the list a few days after the initial posting
identifying the 'feature'.  Join those of use who have put in a feature request
for a safe and complete 'compress partition' command or oncheck option and maybe
we'll see it in 9.6 or so.

Art S. Kagel