IntermediateScenario
10 min
Database Connection Exhaustion
DatabasesConnection PoolingTroubleshooting
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Interview Question
Your application logs show frequent database connection pool exhaustion errors. How do you investigate and fix this?
Key Points to Cover
- Check DB pool settings vs workload
- Inspect for unclosed connections or long-running queries
- Increase pool size or optimize queries as needed
- Add caching or read replicas to reduce load
- Configure timeouts and retries properly
Evaluation Rubric
Analyzes connection pool usage30% weight
Identifies query/connection issues30% weight
Proposes tuning or scaling fixes20% weight
Mentions caching/replica strategies20% weight
Hints
- 💡Check ORM connection leak issues.
Common Pitfalls to Avoid
- ⚠️Only increasing `maxPoolSize` without understanding the underlying cause.
- ⚠️Focusing solely on application code and neglecting database-level performance issues (e.g., missing indexes).
- ⚠️Not using proper try-catch-finally or try-with-resources blocks to ensure connections are always closed.
- ⚠️Ignoring the `connectionTimeout` setting, which can lead to applications waiting indefinitely for a connection that will never become available.
- ⚠️Failing to set appropriate `idleTimeout` and `maxLifetime` values, which can lead to stale connections being kept in the pool.
Potential Follow-up Questions
- ❓How would you tune pool sizes?
- ❓What about retry storms?
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