Learning series · 4 episodes · Staff / Senior
The copies disagree
Five connected lessons on WAL replay visibility, session freshness, quorum boundaries, tombstone repair, and replica fanout.
Start series →Follow the decisions in order
- Part 1 of 5
Staff
The follower has the commit record. Why is the read still old?Distinguish WAL receive, durable flush and replay visibility, and gate reads on a reliable apply boundary.
- Part 2 of 5
Senior
The profile saved. Why does your laptop still show the old name?Define scope of read-your-writes and design client or account-level consistency tokens with fallback behavior.
- Part 3 of 5
Staff
Two of three replicas agreed. Why did a later read return older data?Distinguish quorum intersection from monotonic reads and linearizability under partially applied or concurrent writes.
- Part 4 of 5
Principal · AI Engineering reading
We deleted a customer record from Cassandra. Why did repair bring it back?Connect deletion markers, grace periods, compaction, repair and offline replica rejoin into one correctness contract.
- Part 5 of 5
Staff
We added twenty read replicas. Why did the primary get slower?Diagnose write-history fanout, WAL-retention pressure, standby feedback and alternative read architectures.