The set of reachable vc values are consistent states

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Unformatted text preview: sistent states of the computation. Redraw previous example (sequence of RPCs) using vector clocks. p1, p2, p3: p2-­‐>p1, p1-­‐>p3, p3-­‐>p1, p3-­‐>p2, p1-­‐>p2, p1-­‐>p3 p2 does RPC to p1; p1 does RPC to p3; p3 replies to p1; p3 does RPC to p2; p1 replies to p2; p1 does RPC to p3 Various states are possible (valid): if an event is included, then all of the events that happen before it are included. An application of this idea: consistent snapshot [Chandy, Lamport. Consistent Snapshots. 1985] “The … algorithm plays the role of a group of photographers observing a panoramic, dynamic scene, such as a sky filled with migrating birds-a scene so vast that it cannot be captured by a single photograph. The photographers must take several snapshots and piece the snapshots together to form a picture of the overall scene. The snapshots cannot all be taken at precisely the same instant because of synchronization problems. Furthermore, the photographers should not disturb the process that is being photographed; for instance, they cannot get all the birds in the heavens to remain motionless while the photographs are taken. Yet, the co...
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