Undo for Sysadmin
3 cases needing Undo
- Reverse the effects of a mistyped command (rm –rf *)
- Roll back a software upgrade without losing user data
- “Go back in time” to retroactively install virus filter on email server; effects of virus are squashed on redo
The 3 R’s vs. check pointing, reboot, logging
- Check pointing gives Rewind only
- Reboot may give Repair, but only for “Heisenbugs”
- Logging can give all 3 R’s
- but need more than RDBMS logging, since system state changes are interdependent and non-transactional
- 3R-logging requires careful dependency tracking, and attention to state granularity and externalized events
(Undo may help with security systems)