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Unformatted text preview: ings? How can I guarantee that if I have no definition of global time? Now, add some caches! FB says they do approx 100 separate lookups per page; can’t possibly go to the server. And they have approx 1M servers, and another 1M caches. This is where Lamport fits in – to help explain what you can say about the order of events in a distributed system. We’ll start with a really simple case: no failures! Messages can only have bounded delay, and all we’re interested in, is making sure multiple hosts come to some common understanding about their shared state. This should be easy, right? Example #1: going out to lunch. Order of operations changes the semantics, so we only have shared knowledge, if we see the same ordering of events. Arranging lunch – value of preserving the causal order. a: how about lunch? meet at 12? b: can’t – meeting. 1pm? c: <receives a>: ok by me d: <receives c>: what’s ok? a: <receives b then c>: which is ok? Solution: if messages are delivered in same order everywhere, no opportunity for confusion. E...
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- Spring '14