Replication

Cards

1. Why is replication between distant regions usually asynchronous? easy Multiple choice
2. A database is overloaded by writes. Why does adding read replicas not help? easy Flashcard
3. A primary takes 5,000 writes/s and replicates asynchronously, with the follower about 2 seconds behind. The primary's disk dies and the follower is promoted. Roughly how many acknowledged writes are lost? medium Estimate
4. Replicating a disk to a standby versus replicating at the application level: what does the second give you? medium Flashcard
5. How do reads and writes work in leaderless (Dynamo-style) replication? medium Flashcard
6. A user sees a new comment, refreshes, and it is gone, because the second read went to a replica further behind. The guarantee that prevents this is _____. medium Fill in the blank
7. When a quorum read finds a replica with an older version and writes the newer value back to it, that is _____. A background process that compares replicas using _____ to find and fix differences is called anti-entropy. medium Fill in the blank
8. A user updates their profile, reloads, and sees the old version because the read went to a lagging replica. That breaks _____ consistency. medium Fill in the blank
9. Synchronous vs asynchronous replication: what does each give up? medium Flashcard
10. How long should followers wait without hearing from the leader before failing over? What does each choice risk? hard Flashcard
11. Replicas resolve conflicts with last write wins by timestamp. What can go wrong? hard Multiple choice
12. With a leader in each region, what new problem appears, and how is it handled? hard Flashcard
13. After a failover with async replication, the old leader comes back with writes the new leader never got. What happens to them, and why is that risky? hard Flashcard
14. A leader has three followers. Which setup keeps writes fairly fast but still guarantees that every acknowledged write is on at least two machines? hard Multiple choice
15. The old leader is cut off by a network partition, a follower is promoted, and now both accept writes. What prevents this split brain? hard Multiple choice