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How would you handle a schema change when new files arrive?

System Design/Architectureeasy0.2 min readPremium

**Approach**: (1) Evolution—additive; new columns default; (2) Validation—quarantine unknowns; (3) Versioning—tag files; (4) mergeSchema=True for Parquet; (5) Migration—support old+new; update consumers. Schema registry for contracts; coordinate with producers....

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Frequency
Low
Asked at 1 company
Category
179
questions in System Design/Architecture
Difficulty Split
15E|6M|158H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Delivery Hero
Interview Pro Tip

Pro-Move: 'New column "region" arrived. Pipeline added with default null. Backfill job for historical. Both versions supported for 2 weeks.'

Why This Question Matters

This easy-level System Design/Architecture question appears frequently in data engineering interviews at companies like Delivery Hero. While less common, it tests deeper understanding that distinguishes strong candidates.

How to Approach This

Start by clearly defining the core concept being asked about. Interviewers want to see that you understand the fundamentals before diving into implementation details. Structure your answer with a definition, then explain the practical application with a concise example.

Expert Answer
34 words

Approach: (1) Evolution—additive; new columns default; (2) Validation—quarantine unknowns; (3) Versioning—tag files; (4) mergeSchema=True for Parquet; (5) Migration—support old+new; update consumers. Schema registry for contracts; coordinate with producers. Delivery Hero: event schema evolution common.

The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations covering performance optimization and real-world examples.

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According to DataEngPrep.tech, this is one of the most frequently asked System Design/Architecture interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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