3 ms·
Are you referring to this passage? 2. Introducing noise to drive the device out of its metastable state.The noise can be considered to be just an unpredictable
by mannykannot 7y ago
Are you referring to this passage?
2. Introducing noise to drive the device out of its metastable state.The noise can be considered to be just an unpredictable input.The introduction of noise cannot eliminate the possibility of the device hanging up for an arbitrarily long time, but can make it impossible
to predict which inputs will cause it to do so.
While I do not disagree, introducing noise changes the issue from being stuck forever on a single decision, to being a series of decision points (each time the noise signal changes), with the chain being broken as soon as one results in a definite outcome. In practice, this allows us to engineer the risk of being stuck, for longer than some specified period, to an arbitrarily small probability - at the cost of a small loss of precision, and possibly much greater complexity in modeling the device.
- senderista 7y agoCoincidentally, this is reminiscent of the usual solution to Paxos liveness violations: introduce randomness into the timing of the competing proposals.
- shakezula 7y agoTrue! Wouldn’t be surprised if that’s why Lamport was originally thinking about the problem.
- aj7 7y agoNo no no! Using noise is useless without hysteresis. You must have a process, built in, which prevents re-decision or waffling for a time sufficient that conditions are so changed as to eliminate the original decision. Once you stop, you stop long enough for the train to pass. Or you close your eyes and floor it, and stand on the accelerator.