Question 1

Explain wide vs. narrow transformations and how they drive shuffle cost, failure domains, and pipeline design. When would you intentionally add a wide transformation, and how do you minimize its impact?

Accepted Answer

**Section 1 — The Context (The 'Why')**
Wide transformations force full data shuffles across the cluster; narrow transformations stay partition-local. The cost of shuffle dominates Spark job runtime at scale.

**Section 2 — The Diagram**
```
[Narrow: map, filter] --> [RDD] --> [Wide: join, groupBy] --> [Shuffle]
```

**Section 3 — Component Logic**
**Narrow transformations** (map, filter) do not require data movement....

Question 2

Data masking scenarios for secure data handling

Accepted Answer

**Scenarios**: (1) PII in dev—mask SSN, email, names. (2) Logs—redact tokens. (3) Exports—generalize (region vs. city). (4) Support—dynamic masking (last 4 of card). **Techniques**: Substitution, hashing, blurring....

Question 3

Normalization: Various forms and impact on query performance

Accepted Answer

Higher normalization (3NF) often increases joins, which can slow queries. Denormalization (star schema) reduces joins, improves read performance. Balance: normalize for source/ODS; denormalize for warehouse reporting. Materialized views can denormalize without base-table redundancy. **Why it matters**: Design choices compound at scale—wrong approach can cause 100× overhead. **Scalability trade-offs**: Profile before optimizing; validate on sample then full....

Question 4

Optimization: Performance tuning strategies and temporal tables

Accepted Answer

Performance: indexing, partitioning, query rewrite, statistics. Temporal tables: system-versioned tables for point-in-time queries. Use for auditing, history. Example: SELECT * FROM employee FOR SYSTEM_TIME AS OF '2024-01-01'. Combines current and historical in one query. **Why it matters**: Design choices compound at scale—wrong approach can cause 100× overhead. **Scalability trade-offs**: Profile before optimizing; validate on sample then full....

Question 5

SCDs: Types of Slowly Changing Dimensions and their use cases

Accepted Answer

SCD types: 1—overwrite (no history); 2—add row (full history); 3—add column (previous value). Type 4—separate history table. Type 5—mini-dimension. Type 6—hybrid. Use 1 for corrections; 2 for audit/history; 3 for single previous value. Type 2 most common in DW. **Why it matters**: Design choices compound at scale—wrong approach can cause 100× overhead. **Scalability trade-offs**: Profile before optimizing; validate on sample then full....

Question 6

Schema Design: Star vs. Snowflake schema differences

Accepted Answer

**Section 1 — The Context (The 'Why')**
The primary challenge for this design in SQL is balancing scale, cost, and reliability. At scale, naive approaches fail: single points of failure cause cascades, schema evolution breaks consumers, and over-provisioning explodes cost. Failure modes include silent data loss from non-idempotent writes, cascading job failures from tight coupling, and operational burden from manual intervention....

Question 7

Spark optimizations: Partitioning, caching, tuning parallelism

Accepted Answer

Spark: partition by key (date, id) for pruning and join locality. Cache: cache() for repeated use. Parallelism: spark.default.parallelism = 2–4 * cores; repartition for shuffle. Tuning: executor memory, cores, shuffle partitions. AQE for adaptive optimization. Monitor Spark UI for skew and GC. **Why it matters**: Design choices compound at scale—wrong approach can cause 100× overhead. **Scalability trade-offs**: Profile before optimizing; validate on sample then full....

Question 8

Apache Spark Architecture - RDD, DAG, cluster manager, driver node, worker node

Accepted Answer

**Section 1 — The Context (The 'Why')**
The primary challenge for this design in Spark/Big Data is balancing scale, cost, and reliability. At scale, naive approaches fail: single points of failure cause cascades, schema evolution breaks consumers, and over-provisioning explodes cost. Failure modes include silent data loss from non-idempotent writes, cascading job failures from tight coupling, and operational burden from manual intervention....

Zen Data Shastra Data Engineer Interview Questions

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Zen Data Shastra Data Engineer Interview Questions

+13 More Questions with Expert Answers

Other Companies