AdvancedTechnical
5 min
Zero-Downtime Database Migration Strategy
DatabasesScalabilityMigrations
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Interview Question
Describe your approach for performing a zero-downtime database migration in production.
Key Points to Cover
- Use expand-contract pattern: deploy schema changes safely
- Enable dual writes temporarily when moving data between tables
- Leverage feature flags to manage rollout safely
- Run load tests and dry runs before applying changes
Evaluation Rubric
Applies correct zero-downtime techniques30% weight
Mitigates risks with rollout control30% weight
Includes tests and dry runs20% weight
Monitors database health actively20% weight
Hints
- 💡Backfill asynchronously and phase out old schema carefully.
Common Pitfalls to Avoid
- ⚠️Insufficient testing: Not adequately testing migration scripts or application compatibility with the new schema.
- ⚠️Lack of a rollback plan: Failing to have a clearly defined and tested procedure to revert to the previous state if something goes wrong.
- ⚠️Underestimating data consistency challenges: Not accounting for race conditions or data inconsistencies during dual writes or shadow writes.
- ⚠️Ignoring application dependencies: Not considering how the migration might impact other services or downstream applications that rely on the database.
- ⚠️Inadequate monitoring: Not setting up proper alerts or metrics to detect issues in real-time post-migration.
Potential Follow-up Questions
- ❓How would you handle migration rollbacks?
- ❓How do you prevent deadlocks during migrations?
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