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How do you manage event schema evolution without breaking reports?
Backward-compatible serialization, nullable new fields, raw versus modeled layers, versioned schemas, and consumer alerts.
What are the challenges of grouping by a high-cardinality dimension?
Tests columnar storage internals and query engine scalability. A strong answer covers memory pressure from giant hash tables, destroyed compression ratios, and massive result-set overhead.
How do duplicate events bias COUNT(*) and daily login reports?
Tests idempotency in streaming analytics. COUNT(*) overcounts; fix with unique event ID dedup via idempotent writes or COUNT(DISTINCT id), plus daily partition reconciliation. Red flag: SELECT DISTINCT * without a stable key or no reporting safeguard.
Why is star schema preferred over 3NF for analytics?
Tests your grasp of the read-performance trade-off in analytical schemas. A great answer names fact and dimension tables, emphasizes fewer joins for aggregations, and cites simpler SQL and faster query plans.
Slow dashboard querying a large fact table: first three checks?
This tests systematic diagnosis of fact-table query latency. A strong answer checks the execution plan and indexing, evaluates partitioning and data model fit, and inspects caching or pre-aggregation.
Why prefer median and p95 over mean for API latency?
This tests statistical intuition for skewed distributions. A strong answer notes that median captures typical experience, p95 captures tail suffering, and mean hides outliers. A red flag is claiming mean alone is sufficient.
Design a scalable data governance framework balancing autonomy and control
Self-serve platform with domain products, auto-catalog, schema contracts, and policy-as-code access in CI/CD.
How do you root-cause bad data across microservices and Spark?
This tests structured debugging and observability for distributed pipelines. A strong answer isolates the break via lineage, validates schema and freshness per stage, and compares microservice outputs to Spark inputs.
How would you build a Customer golden record across fragmented systems?
This tests master data management discipline for distributed, conflicting records. A strong response covers identity resolution, survivorship rules, merge architecture, lineage, and feedback loops.
Design a CDC pipeline that handles schema evolution gracefully
Tests designing resilient CDC pipelines against schema drift. A strong answer covers schema registries with versioning, backward-compatible serialization, and automated compatibility checks.
How would you implement data lineage for microservices analytics?
Tests end-to-end provenance tracking, not just docs. Strong answers cover automated metadata capture at service boundaries, a central catalog such as DataHub or OpenLineage, and column-level tracing.
What is a data schema and why enforce it at ingestion?
Tests schemas as contracts and ingestion validation as a quality gate. Strong answers cite blueprints with constraints, fail-fast ingestion catching type errors upstream, and downstream trust. Red flag: treating schemas as optional docs affecting only storage.
What validation checks would you implement for a user-submitted email field?
Tests whether you separate syntax validation from deliverability and know practical ingestion guards. A strong answer covers RFC-aware syntax, domain checks, normalization, and deduplication.
How do you handle 10% nulls in a key numerical column?
Check MCAR/MAR/MNAR; prefer median or mean imputation; add an "is_missing" indicator.
Design a data quality framework from source to consumption
This tests full-lifecycle data architecture. Strong answers define ownership first, then schema contracts at ingestion, profiling and anomaly detection in CI/CD, column-level lineage, and KPI-linked scorecards. Red flag: tools before ownership or RACI.
Diagnose out-of-memory errors in a growing Spark job
Inspect plans for skewed partitions and joins; tune shuffle partitions, batch sizes, and join strategies; leverage AQE and statistics.
What is data partitioning in a cloud data warehouse?
Tests physical data layout and cost/performance tradeoffs. Strong answers define time-based or integer-range partitioning, explain partition pruning avoids full scans, and warn against high-cardinality keys.
How would you handle late-arriving data in a streaming analytics pipeline?
Tests understanding of event-time processing, watermarks, and windowing for correctness. A strong answer covers watermarks with allowed lateness, event-time triggers, and idempotent updates to sinks.
Describe star and snowflake schemas and their trade-offs
Star schemas flatten dimensions for fast joins; snowflake schemas normalize hierarchies to reduce redundancy but add joins.
Explain data warehouse purpose and how it differs from OLTP
This tests whether you know the OLTP versus analytics split. A great answer contrasts OLTP row-level writes and normalized schemas with warehouse denormalized schemas and BI reads. A red flag is calling a warehouse just a bigger OLTP database.