Question 1

How do you handle schema mismatches during merging?

Accepted Answer

**Strategies**: (1) Schema evolution—additive; defaults; (2) unionByName(allowMissingColumns=True) in Spark; (3) Mapping—explicit column mapping; null for missing; (4) Validation—quarantine incompatible; (5) Versioning—tag with schema version....

Question 2

What are the limitations of Assert Transformations in complex data flows?

Accepted Answer

Limitations: (1) Single-dataset—hard to express cross-table. (2) Performance—full scan per assertion. (3) Granularity—row vs aggregate; complex rules need custom. (4) Order—upstream changes break. (5) Reporting—limited context (partition, key). (6) Schema evolution—manual updates....

Question 3

How do you ensure fault tolerance during large-scale data migrations?

Accepted Answer

**Section 1 — The Context (The 'Why')**
Fault-tolerant data migration must handle large volumes, schema mapping, and cutover with minimal downtime. The primary challenge is consistency during dual-write and validation....

Question 4

How do you pass global variables between pipelines?

Accepted Answer

**Section 1 — The Context (The 'Why')**
The primary challenge in 'How do you pass global variables between pipelines?' centers on designing for production scale, correctness guarantees, and operational resilience. A naive or underspecified design fails under load: single points of failure cascade, non-idempotent operations cause duplicates on retry, and lack of observability blocks root-cause analysis....

Question 5

How do you use dependency tracing to identify root causes in pipeline failures?

Accepted Answer

**Section 1 — The Context (The 'Why')**
The primary challenge in 'How do you use dependency tracing to identify root causes in pipeline failures?' centers on designing for production scale, correctness guarantees, and operational resilience. A naive or underspecified design fails under load: single points of failure cascade, non-idempotent operations cause duplicates on retry, and lack of observability blocks root-cause analysis....

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Virtusa System Design Interview Questions

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