Vector clock

Source: Wikipedia Topic: Capturing causality and concurrency in distributed systems.

Core idea

Vector clocks refine simple logical clocks by distinguishing causal order from genuine concurrency.

Key claims

• Not all “later” events are causally later.
• A useful system should distinguish happened-before from concurrent updates.
• Merge and replay logic improve when concurrency is represented explicitly rather than flattened into timestamp order.

Harness takeaway

A harness should carry causal frontiers on work objects and projections so it can tell independent branches from true conflicts.