A Partial Event Ordering for Distributed Systems(Lamport 1978)

• Absence of central time means: no notion of happened-when (no total ordering of events)

• But can generate a happened-before notion (partial ordering of events)

• Happened-Before relation:

1. Pi

a

b

Event a happened-before Event b. (a -> b)

2. Pi

a

Event a happened-before Event b. (a -> b)

Pj

b

3. Pi

a

Event a happened-before Event c. (a -> c) (transitivity)

Pj

b

c

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