lindsay@gandalf.cs.cmu.edu (Donald Lindsay) (01/28/91)
<NOTE THE FOLLOWUP-TO> In article <1991Jan27.003821.24814@unx2.ucc.okstate.edu> minich@unx2.ucc.okstate.edu (Robert Minich) writes: >With a log based editor, what happens if someone changes the file while >you're editing it? Are the files locked while in use? One answer is locks. Unix didn't offer that, so some editors (on exit) check that the original's last-modification-date is still the same. There is a _lot_ of OS literature arguing that files (except for data bases) should be unmodifiable. When someone writes one, they are always creating a new file. If an old file of the same name existed, then the old and new files coexist, and are told apart by OS- generated version numbers. This has interesting media advantages - it meshes well with WORM technology. It does some good things to distributed environments, making things more atomic, more nameable. It's also convenient - "undo" == "delete latest". Users get some policy control: TOPS-20 allowed a keep amount (e.g. 3) to be set per-directory, etc. Our backup tools automatically migrated old versions to tape. In short, it was pretty well win-win. -- Don D.C.Lindsay .. temporarily at Carnegie Mellon Robotics