Question 1

What is the difference between OLTP and OLAP?

Accepted Answer

**Why the distinction exists**: They serve different access patterns. OLTP = many small, random writes and point reads. OLAP = few, large sequential scans and aggregations. Optimizing for one degrades the other. **OLTP**: Row-oriented storage (fast single-row access). Normalized schema (3NF) to avoid update anomalies. Indexes for lookup (B-tree). ACID for consistency. High concurrency via locking/mvcc. Examples: PostgreSQL, MySQL, Oracle....

Question 2

What is the difference between SQL and NoSQL databases?

Accepted Answer

**Why both exist**: SQL excels at structured data, complex joins, and strong consistency. NoSQL excels at unstructured/semi-structured data, horizontal scale, and flexible schema. **SQL (relational)**: Fixed schema, ACID, vertical scale (or managed horizontal via Citus, etc.). Optimized for joins and aggregations. Best for: transactional systems, reporting, anything requiring referential integrity. **NoSQL**: Schema-flexible, BASE (eventual consistency), horizontal scale....

Question 3

Are you open to learning new tools and technologies?

Accepted Answer

**STAR**: Situation: Data engineering evolves rapidly. Task: Stay current. **Action**: I learn via docs, courses, side projects. Recently picked up Terraform, Delta Lake. I dedicate time weekly. I volunteer for POCs with new tech. **Result**: Delivered 3 projects on tools I had never used before by ramp-up....

Question 4

Describe your approach to managing data deduplication.

Accepted Answer

**Architectural Logic**: Deduplication is layered—at ingest (constraints/upserts), batch (deterministic selection), and stream (exactly-once semantics with dedup windows).

**Why Layered**: Ingest prevents duplicates early; batch handles historical drift; stream semantics handle retries and late arrivals.

**Implementation**: Use MERGE/INSERT OVERWRITE with dedup keys; ROW_NUMBER() OVER (PARTITION BY key ORDER BY updated_at DESC) for batch; event IDs + content hashes for idempotency....

Question 5

How would you incorporate data security and access control?

Accepted Answer

Data security uses defense-in-depth with clear architectural layers. WHY: Single-layer security fails; compliance (SOC2, HIPAA, GDPR) mandates layered controls. AUTHENTICATION: Integrate IdP (Okta, Auth0) or IAM; enforce MFA for production. AUTHORIZATION: RBAC—roles (analyst_read, engineer_write) with minimal permissions; column-level and row-access policies for PII. ENCRYPTION: At rest (AES-256) and in transit (TLS 1.2+). AUDITING: Access logs, CloudTrail, lineage....

Question 6

Walk me through your resume.

Accepted Answer

Chronological or thematic. Current: 'I'm [title] at [company]; [2-3 responsibilities]; recently [achievement].' Prior: duration, key outcomes. 2–3 min. End: 'That brings me to why I'm excited about this opportunity.' Emphasize progression, technical depth, outcomes.

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Fragma Data Systems General Interview Questions

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