Logical clocks
·1 min
- How to reconcile logical clocks with wall clocks?
- Two algorithms:
- Lamport.
- Total order, consistent with causality.
- Vector clocks. Related but not same as version vectors.
- Q: how to merge two event timestamps?
- Q: how to compare?
- How to find incomparable?
- Timestamps summarize everything that happened before.
- Lamport.
- Partial vs total order:
- Partial == happens before: order
onlybetween causal events, none between concurrent. Basically, some events are incomparable. - Total: order defined for each pair of events.
- Partial == happens before: order
- Timestamps are incremented before message sent to another node and when received.