Comparison
Monotonic readsvsRead-your-writes consistency
Monotonic reads
the page shows the new comment, you refresh, it disappears, you refresh again and it is back, because you hit three different replicas.
The guarantee that a client never sees time move backwards: once it has read a value, subsequent reads do not return older state. It breaks when consecutive requests land on replicas with different lag. Sticky routing per session is the usual fix, and it costs you a little load balancing freedom.
Full entry →Read-your-writes consistency
the user updates their profile, the page reloads from a replica, and their change is missing for two seconds.
A guarantee that a client always sees its own prior writes, even under eventual consistency elsewhere. It is usually implemented by routing that user's reads to the leader for a short window, or by tracking a write timestamp and waiting for a replica to catch up. Skipping it is the single most common source of "the save button doesn't work" bug reports.
Full entry →