A social app has mobile users across several cities. Each user's own writes must appear immediately in that user's later reads, while other users may see slightly older data. Which Cosmos DB consistency level meets this requirement?
Show answer and explanation
Answer: A
Session consistency scopes its guarantees to one client session, so a user always reads their own writes and sees progress that never goes backwards, while other sessions may lag. It is the default level in Cosmos DB and performs well because it avoids cross-region coordination on every read. Eventual gives no read-your-writes promise, consistent prefix only ensures ordering, and bounded staleness limits lag for all clients rather than guaranteeing a particular user's writes.
Why the other options are wrong
- B. Eventual consistency offers no promise that a user will see their own recent write, so the app could show stale data right after a save.
- C. Consistent prefix keeps writes in the order they were made but does not promise that a user's latest write is visible in their own next read.
- D. Bounded staleness limits how far every reader can lag behind writes, yet it does not give a single user read-your-writes behaviour as the requirement asks.