version numbers, or: Gimme that old-time religion!

[David Vinayak Wallace <Gumby@mc.lcs.mit.edu>]

This message has nothing to do with lisp machines at all.

    Date: Thu, 19 Nov 87 23:45:34 -0500
    From: Rayan Zachariassen <rayan%ai.toronto.edu@RELAY.CS.NET>

    # You could also use a filesystem with version numbers.  I cannot
    # understand how, in this day and age, people still advocate a
    # filesystem which has not caught up with the 1960's.

    Never having lived on a filesystem with version numbers (except on lispm's,
    where I mostly turn it off),

How do you "turn it off?"
				 it isn't clear to me why this is a good philosophy.
    Could someone enlighten natives of the non-version number filesystems?

				 ...what are the overhead costs, and are they
    worthwhile compared to other approaches (from both system & user pt. of view)?

Well, the one "disadvantage" of a version-number filesystem is that it
takes up a little disk space.  If you have generation-retention control
(i.e. keep only the last n versions) this isn't really a problem at all.
User overhead is essentially nil (just ignore them when specifying a
filename and let the system do the right thing).

    What do people use it for, that makes it worthwhile?

It allows you to keep track of changes.  If you find you've happily been
editing all day and suddenly discover you've made some gross error, what
do you do?  Under unix, you're scrod; the best you can hope for is that
you used something like RCS and manually checked it out, or otherwise
kept a checkpointed copy somewhere.  But that doesn't give you much
granularity.  You can't back off the change you "just made."  If you
don't have version numbers you have to take manual action to protect
yourself, which of course you'll fail to do just before you need to
have!

It's not just humans which lose it, either.  Programs go berzerk; it's
nice to be able to delete a trashed file and go back to the previous
version.  Why should every program have to make allowances for this?

Hard links aren't very useful in a system with version numbers, but
normal links are.

Of all the missing features of the unix filesystem (e.g. don't-reap and
backup bits, don't-exist-until-closed, locks, undeletion), version
numbers are the most infuriating.