Interview › Databases & Caching
What is synchronous versus asynchronous replication, and the trade-offs?
Databases & Caching · Intermediate level
Answer
Synchronous replication waits for a replica acknowledgement before commit returns, reducing data-loss risk but increasing latency. Asynchronous replication returns faster but permits replica lag and possible data loss during failover.
Technical explanation
WAL/binlog volume affects storage, backup, replica lag, and restore behavior.
Near-zero downtime migration requires initial load, CDC, validation, short write drain, cutover, and rollback planning.
DMS helps move data, but schema conversion, application compatibility, and data validation remain engineering responsibilities.
Hands-on example
Migration runbook:
1. Create target database and schema.
2. Start full-load plus CDC using DMS or logical replication.
3. Monitor lag and task errors.
4. Compare row counts and critical aggregates.
5. Stop writes briefly.
6. Wait for lag to reach zero.
7. Switch endpoint/secret.
8. Monitor app errors and DB load.
9. Keep source read-only until rollback window closes.
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