How would you test the performance impact of a database migration?
- database migration
- benchmarking
- zero-downtime
Answer it first, then compare. Nothing here is saved or scored.
Model answer
Before migration: (1) Benchmark current query performance and throughput. (2) Test migration on a production-scale copy of the database, not a small test database. (3) Measure migration execution time and lock duration. During migration: (4) Test that the application remains available (zero-downtime migration). (5) Monitor query performance during the migration. After migration: (6) Re-run performance benchmarks and compare. (7) Test with production-like data volume. Key: always test migrations with realistic data sizes, a migration that takes 1 second on test data might take 30 minutes on production.
What interviewers listen for
- Workload modellingYou design the load shape from product traffic, not from tool defaults.
- Percentile literacyYou read p50/p95/p99 separately and explain why each matters.
- Bottleneck triageYou correlate metrics across application, database, and infrastructure layers.
- Capacity instinctsYou can translate a soak test into a sizing or scaling recommendation.