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Re: subversion as a low-level filesystem

From: Steve Greenland <steveg_at_lsli.com>
Date: 2005-02-16 18:40:58 CET

On Wed, Feb 16, 2005 at 09:13:45AM -0500, Jeffrey Vaughan wrote:
> Jos? Moreira wrote:
> >Hello, i was wondering about the viability of the implementation of a
> >'version controller' filesystem (kernel level). I believe that something
> >like that could be as or more useful that WinFS or similar. Anyone has
> >an opinion? thanks
>
> The VMS filesystem, iirc, was versioning.

Mmmm, kinda sorta. It would keep multiple versions of files, indicated
by a trailing ';N' on the file name; e.g. foo.txt;1, foo.txt;2, etc.
Sometimes useful (editor), sometimes *extremely* annoying (program that
logged to a file every few minutes by opening, appending, and closing.)

- You could set attributes on a file so that would keep only a specified
number of versions. You could set this on the directory level, so
any *new* files inherited it.

- The obscure bad thing was that the version number was limited to
32767. The next time you opened and tried to write the file, it would
fail. You could fix this by renameing the file to a lower version number
(e.g. "rename foo.log;32767 foo.log;1"), but you had to be careful
because:

- When you accessed "foo.txt", it would open the *highest numbered*
file, not necessarily the newest. So not only did you have to rename
the highest versioned one, but delete all the other ones. this was also
problematic, because:

- If you forgot to set the maximum number of versions to keep,
you ended up with 32766 files to delete. If you did the obvious
"delete/exclude=foo.log;1 foo.log;*" (well, obvious on VMS, anyway) it
would take friggin' *forever*, because directories were store in lexical
order, and had to be rebuilt if you deleted an intermediate entry, so
the above command would cause a directory re-build for every single
file. Deleting from the end was cheap and fast, though, so everyone
had/wrote/stole a script to loop through file entries in reverse order.

Subversion it was not.

More VMS Fun Facts on request,
Steve

-- 
"Outlook not so good." That magic 8-ball knows everything! I'll ask
about Exchange Server next.
                           -- (Stolen from the net)
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Received on Wed Feb 16 18:54:32 2005

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