Fast forward-backward (write-read)

[Paul Rubin]

Virgil Stokes <vs at it.uu.se> writes:
> Yes, I do wish to inverse the order,  but the "forward in time" file
> will be in binary.

I really think it will be simplest to just write the file in forward
order, then use mmap to read it one record at a time.  It might be
possible to squeeze out a little more performance with reordering tricks
but that's the first thing to try.