Explain Aurora-style internals: WAL, MVCC, replication, recovery

## Database Internals Deep Dive You are interviewing for a cloud database engine team (Aurora-like). Answer conceptually and with trade-offs. ### Questions 1. **Architecture**: How does a cloud-native database architecture (separating compute from distributed storage) differ from a traditional single-node database using local disks? What are the benefits and costs? 2. **Replication model**: Compare replication approaches: - physical vs logical replication - statement-based vs row-based vs log-based - synchronous vs asynchronous - quorum-based durability in distributed storage When would you choose each, and what failure modes do they address? 3. **WAL / redo log**: What is the role of WAL (write-ahead logging) in durability and crash recovery? How do redo/undo relate to WAL? What must be forced to durable storage on commit? 4. **Crash recovery**: Walk through a typical recovery procedure after a crash (phases, checkpoints, replay). What changes when storage is distributed? 5. **MVCC**: Explain MVCC fundamentals: - how reads avoid blocking writes - snapshot visibility rules (high level) - what metadata is stored per row/version 6. **High-concurrency writes**: Under heavy write load, how do lock conflicts happen and how can an engine reduce contention (e.g., latches vs locks, optimistic CC, partitioning/hotspot mitigation)? 7. **Trade-offs**: Discuss consistency vs latency vs throughput trade-offs in replication and commit paths (e.g., quorum write, 1-RTT vs 2-RTT commit, read-your-writes, failover behavior).