Which statement best describes causal consistency?

Which statement best describes causal consistency?

• A. A model that guarantees global ordering of all events across the entire system.
• B. A middle-ground consistency model that ensures causally related events appear in the same order to all users, without requiring global ordering of all events.
• C. A mode where readers always see the latest write immediately.
• D. A locking strategy that prevents any concurrent writes.

Answer: (B)

Causal consistency is about preserving cause-and-effect relationships across a distributed system. In this model, if one operation causally influences another, every observer must see those two operations in the same order. But there’s no requirement for a single global order for all operations; unrelated actions can be observed in different orders by different clients. This is why the statement that best describes causal consistency says: causally related events appear in the same order to all users, without requiring global ordering of all events. It captures the essential idea—that the system respects the cause-and-effect linkages—while allowing more flexibility than a full global order. The other ideas describe stronger or different guarantees. Demanding a global order of all events is stricter than causal consistency. Requiring readers to see the latest write immediately describes a stronger, real-time or linearizable behavior. Relying on a locking strategy is a concurrency control mechanism, not a consistency model.

Causal consistency is about preserving cause-and-effect relationships across a distributed system. In this model, if one operation causally influences another, every observer must see those two operations in the same order. But there’s no requirement for a single global order for all operations; unrelated actions can be observed in different orders by different clients.

This is why the statement that best describes causal consistency says: causally related events appear in the same order to all users, without requiring global ordering of all events. It captures the essential idea—that the system respects the cause-and-effect linkages—while allowing more flexibility than a full global order.

The other ideas describe stronger or different guarantees. Demanding a global order of all events is stricter than causal consistency. Requiring readers to see the latest write immediately describes a stronger, real-time or linearizable behavior. Relying on a locking strategy is a concurrency control mechanism, not a consistency model.