ScalingBeginner
Why does a user see their own change revert?
“After adding read replicas, users report seeing old data right after saving. Explain.”
What this tests
- Replication lag
- Read routing
Answers by level
Read the beginner answer first and notice what is missing.
Asynchronous replication means replicas are briefly behind the primary. The write went to the primary; the immediate read went to a lagging replica that had not replayed it yet — a "read your own writes" violation. It is not a bug in the database; it is what async replication means.
Fix by routing a session’s reads to the primary for a few seconds after a write, or waiting for the replica to reach the write’s WAL position.
Green flags · Red flags
Strong green flag · Explains it is expected behaviour, not a fault.
Green flags
- Names replication lag
- Read-your-writes routing
- Knows it is inherent to async
Red flags
- Blames caching
- Wants to make all replication synchronous
Follow-up questions
F1
How do you guarantee a user sees their own write?
Scenario
A profile edit reverts on refresh but is correct 3 seconds later. What changed recently and how do you fix it?