Strong Consistency (Single-Region Raft) Versus Eventual Consistency
TradeoffDistributed SystemsMidSeniorUpdated
Shopping cart service for a global e-commerce site. Users add items from mobile, web, and tablet; some sessions are offline.
Short answer: Eventual consistency (multi-master + CRDT merge). Cart UX tolerates 'union of all adds' semantics, and users hate write failures.
The Two Options
A
Strong consistency (single-region Raft)
B
Eventual consistency (multi-master + CRDT merge)
Drill This: Your Pick First
The Better Pick
Option B
Eventual consistency (multi-master + CRDT merge)
Cart UX tolerates 'union of all adds' semantics, and users hate write failures. The original Dynamo paper picked exactly this trade for Amazon's cart. CRDTs make merges deterministic.
When the Other One Wins
Strong consistency (single-region Raft)
For an inventory decrement or a bank balance, strong consistency wins: silently merging two debits is worse than rejecting one.