Alvaro Herrera <alvherre@commandprompt.com> writes:
> In CVS HEAD there is a pg_freespacemap contrib module that may do what
> you need. You'd have to "backport" it to 8.1 though; it doesn't compile
> as-is.
Looking at the CVS history, I think the main point is that freespace.c
did not formerly expose its internal data structures; the patch moved a
lot of declarations into freespace.h so that the contrib code could get
at them. You'd need to modify the 8.1 sources, but not by much.
regards, tom lane