CS 262 a

(1) True/False [14 points, 2 each] For each answer provide a one sentence explanation. a) Aries could do " time travel " if you kept the whole log and a set of archived snapshots. True. Time travel is the ability to go back to previous point in " serialization " time (which is well defined for ACID transactions). You can start from a fuzzy snapshot and roll forward to the target time using the redo log entries. b) It is easy to add congestion control to UDP by implementing the sliding window protocol (from TCP) at user level. False. It is possible to implement the protocol, but it is difficult to get the congestion control to work since the user-level process may not be scheduled for a long time. c) LRVM would benefit from compiler support. True. set-range calls are error prone and could be better enforced with compiler support (as mentioned in the paper). d) Active messages are a good way to reach the maximum bandwidth of the underlying link. False. Active messages are small and thus have a great deal of space overhead that limits their bandwidth (covered some in the U-Net paper). e) A hypervisor could use lottery scheduling to allocate physical pages among guest OSs. True. This is actually a decent idea, as the hypervisor needs some way to make allocation decisions, and lottery scheduling is a generic mechanism. f) TCP can easily achieve the full bandwidth of a WiFi connection.