Advanced Cloud
Background
Distributed Systems => Distributed Algorithms
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l Fault tolerance (consistency) is the keyword
l What’s the most difficult program you have ever written?
l Concurrent and Distributed programs l Algorithm vs Protocol
Theoretical System Model: Synchrony Assumption
Protocol Design Difficulty
Asynchronous
No upper bound on the delay D of messages
— eventually can be completely dead or just take
long, you never know
Partial Synchrony
There is a theoretical upper bound on D, but you don’t know its value
— you know eventually the problem is gone or the network must back to normal
Semi Synchrony
Assume there is known probability distribution on D
D ~ N(x,y)
Weak Synchrony
Delay D is varying, but it grows polynomials in t
Full Synchrony
All messages are delivered in