Implications
A Lamport clock may be used to create a partial causal ordering of events between processes. Given a logical clock following these rules, the following relation is true: if then, where means happened-before.
This relation only goes one way, and is called clock consistency condition: if one event comes before another, then that event's logical clock comes before the other's. The strong clock consistency condition, which is two way (if then ), can be obtained by other techniques such as vector clocks. Using only a simple Lamport clock, only a partial causal ordering can be inferred from the clock.
However, via the contrapositive, it's true that implies . So, for example, if then cannot have happened-before .
Another way of putting this is that means that may have happened-before, or be incomparable with in the happened-before ordering, but did not happen after .
Nevertheless, Lamport timestamps can be used to create a total ordering of events in a distributed system by using some arbitrary mechanism to break ties (e.g. the ID of the process). The caveat is that this ordering is artifactual and cannot be depended on to imply a causal relationship.
Read more about this topic: Lamport Timestamps
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