Database Administrator Interview
Questions & Answers

Identify the slow query with pg_stat_statements or the slow query log, run EXPLAIN ANALYZE to see the execution plan, check for missing indexes on filter and join columns, look for table bloat or stale statistics needing VACUUM/ANALYZE. Fix the query plan before touching the schema, and the schema before adding hardware. Profile first — adding RAM to a database with a missing index is expensive and temporary.

RPO drives backup frequency; RTO drives recovery approach. Full backups daily, WAL archiving for point-in-time recovery. Backups stored in a separate region from production. Test the recovery procedure quarterly — a backup you have never restored is an untested backup. Document recovery runbooks so the on-call engineer at 2am is not improvising.

Clustered index: the table data is physically sorted by this key — one per table, typically the primary key, fast for range scans. Non-clustered index: a separate structure with a pointer back to the data row — multiple allowed per table. Over-indexing is a real problem: every index adds write overhead and storage. Add indexes for specific slow queries, not speculatively.

Expand-contract pattern: add the new column (backwards-compatible), deploy the application to write to both old and new, backfill data, switch reads to the new schema, then drop the old in a later deployment. Never run a blocking migration (ADD NOT NULL without a default on a large table) during peak traffic. Use gh-ost or pt-online-schema-change for large table alterations that must happen online.

Key metrics: query latency (p50/p95/p99), connections used vs max, replication lag on read replicas, disk I/O utilisation, slow query rate, and buffer cache hit rate. Alert on sustained replication lag over 30 seconds (a read replica is serving stale data) and connections approaching the max (pool exhaustion is a complete outage). Baseline these metrics during normal operation so anomalies are obvious.

Structure your answer as a 60-second professional narrative: where you have been (your background), what you have done (your strongest achievement), and where you are going (why this role). Lead with your most relevant experience, not your entire career history. End with why you are excited about this specific opportunity.

Choose a genuine weakness that you have actively worked to improve. The structure is: name the weakness → show self-awareness of its impact → describe the concrete step you took to address it → show the improvement. Never say "I work too hard" — interviewers recognise this as evasion and it damages your credibility.

Use the STAR method (Situation, Task, Action, Result) but add a fifth element: what you learned. Choose a real failure, not a disguised success. Show you can take responsibility without making excuses, and demonstrate that the lesson changed your behaviour in a specific, verifiable way.

Be honest but constructive. Acceptable reasons: seeking greater scope, new challenge, skills you can not develop in the current role, or company-level changes (restructuring, direction shift). Never speak negatively about your current employer or manager — it signals you will do the same to the prospective employer in future conversations.

Describe the conflict specifically, show that you sought to understand the other person's perspective, and explain the resolution approach you took. Interviewers are assessing your emotional intelligence and whether you escalate or resolve. Avoid stories where you were right and they were wrong — choose a story where both parties grew.

Describe your specific prioritisation system: impact × urgency matrix, stakeholder alignment, or a specific tool or process you use. Then give an example where you applied it under real pressure. Show that your system is systematic rather than reactive, and that you communicate proactively when priorities change.

Choose an achievement that is specific, measurable, and relevant to the role. Lead with the result ("I reduced our error rate by 40% in 90 days"), then explain the context, challenge, and what you specifically did that drove the result. Show your ownership and impact, not just your team's work.

Be honest about your ambitions while showing that this role is a genuine step in that direction — not a stopgap. Hiring managers want to invest in people who will grow with the organisation. Show that your 5-year goal requires the specific skills and experience this role provides, making your ambition an asset for both sides.

Research before the interview and make the answer specific: cite their product, a recent company development, something about their culture or team, or a professional aspect of this particular role that matches your goals. Generic answers ("I love your values") signal you did not do the research. Specific answers signal genuine interest.

Always have 3–5 questions prepared. Ask about the biggest challenge in this role, what success looks like in the first 90 days, how the team operates, and the interviewer's own experience at the company. Never ask about salary, benefits, or holidays in a first interview. Questions show interest, strategic thinking, and that you care enough to have done research.