Eventual consistency is the property that, given enough time without new updates, all replicas of a piece of data will converge to the same value. Reads may see stale or out-of-order data in the short term, but the system guarantees convergence rather than instantaneous global agreement.

Why it exists

Strong consistency (every read sees the latest write) requires coordination on every write,…

Consensus is the problem of getting a set of distributed processes to agree on a single value despite failures, message delays, and out-of-order delivery. Consensus protocols are the foundation under any replicated state machine, leader election, distributed lock, or strongly consistent database.

The classical guarantees

• Agreement. All correct processes decide the same value.
• Validity.…