Edge Case Handling and Debugging Questions

Covers the systematic identification, analysis, and mitigation of edge cases and failures across code and user flows. Topics include methodically enumerating boundary conditions and unusual inputs such as empty inputs, single elements, large inputs, duplicates, negative numbers, integer overflow, circular structures, and null values; writing defensive code with input validation, null checks, and guard clauses; designing and handling error states including network timeouts, permission denials, and form validation failures; creating clear actionable error messages and informative empty states for users; methodical debugging techniques to trace logic errors, reproduce failing cases, and fix root causes; and testing strategies to validate robustness before submission. Also includes communicating edge case reasoning to interviewers and demonstrating a structured troubleshooting process.

MediumTechnical

0 practiced

Implement a retry strategy for database writes used by your ETL job. Provide pseudocode that demonstrates exponential backoff with jitter, a max retry limit, and integration with idempotent upsert logic (e.g., using a unique key or upsert statement). Discuss when to abort and how to surface failures.

HardTechnical

0 practiced

Production aggregates returned negative counts due to integer overflow. Walk through how you would identify the root cause, write unit/integration tests to reproduce the overflow, patch code to use larger numeric types or checked arithmetic, and perform a safe data migration/backfill to correct existing data with validation and minimal downtime.

HardTechnical

0 practiced

Explain trade-offs and design choices to achieve exactly-once semantics when writing stream results to a data warehouse such as BigQuery. Cover transactional sinks, two-phase commit vs idempotent upserts, offset management, checkpointing, and how to validate correctness and measure whether duplicates still occur.

HardSystem Design

0 practiced

You're integrating with external enrichment APIs. Propose a design to implement circuit-breaker and bulkhead patterns in your ETL connectors: per-API circuit breakers, per-worker bulkheads, timeouts, retry budgets, and fallback behavior. Explain how to test these with fault injection and what metrics and alerts to monitor.

EasyTechnical

0 practiced

Write a unit test (PySpark or ScalaTest pseudocode) that asserts a transformation function handles an empty DataFrame gracefully: returns an empty DataFrame with expected schema and does not throw. Include test setup, creating an empty DataFrame with schema, invoking the transformation, and assertions to verify schema equality and zero rows.

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