Which example illustrates eventual consistency?

Which example illustrates eventual consistency?

• A. A like count showing as 142 instead of 143 for a few seconds.
• B. A bank balance showing exact value after each transaction.
• C. A ticketing system ensuring purchases cannot be double-booked.
• D. An order that is guaranteed to be shipped before payment is processed.

Answer: (B)

Eventual consistency means the system allows temporary divergence between replicas while updates propagate, with the guarantee that all replicas will eventually converge to the same latest state. The like count showing 142 instead of 143 for a few seconds is a classic example: after someone likes something, the increment may be applied on different servers at different times, so some replicas show 142 while others show 143. Given a short delay, the counts merge to the correct final value, reflecting eventual convergence. The bank balance that stays exact after every transaction demonstrates a stronger guarantee: reads always reflect the most recent committed value, which is strong consistency rather than eventual. A ticketing system that prevents double-booking also relies on strict coordination to ensure correctness in one operation, another form of strong consistency. The scenario where an order is guaranteed to ship before payment is processed describes a specific business rule and sequencing, not a data convergence property. So, the example that illustrates eventual consistency is the fleeting discrepancy in the like count that later resolves.

Eventual consistency means the system allows temporary divergence between replicas while updates propagate, with the guarantee that all replicas will eventually converge to the same latest state. The like count showing 142 instead of 143 for a few seconds is a classic example: after someone likes something, the increment may be applied on different servers at different times, so some replicas show 142 while others show 143. Given a short delay, the counts merge to the correct final value, reflecting eventual convergence.

The bank balance that stays exact after every transaction demonstrates a stronger guarantee: reads always reflect the most recent committed value, which is strong consistency rather than eventual. A ticketing system that prevents double-booking also relies on strict coordination to ensure correctness in one operation, another form of strong consistency. The scenario where an order is guaranteed to ship before payment is processed describes a specific business rule and sequencing, not a data convergence property.

So, the example that illustrates eventual consistency is the fleeting discrepancy in the like count that later resolves.