How the interviewer opens it
“Design a cloud data warehouse where customers load large structured datasets and run analytical SQL. Different teams need to use the service at the same time.”
The prompt is vague on purpose. The first minutes are for you. Reduce the prompt to the core features and agree on the numbers before you draw.
What to clarify first
- Data scale and retention
- Data loads and retries
- Request mix
- Query shape
- Latency
- Concurrent workloads
- Consistency and availability
- Durability and failures
- Compute lifecycle
- Scope limits
The interviewer has the answers. In a SysRound round, Alex gives these answers, as a real interviewer does.
Scope of a strong answer
Core requirements
- Load structured data in batches.
- Run analytical SQL with filters, joins, and aggregates.
- Give concurrent workloads separate compute capacity.
- Resize or suspend compute without data loss.
Usually out of scope
- Row updates and row transactions.
- Continuous data streams.
- Implement a complete SQL compiler.
- Operate across multiple regions.
What interviewers ask about
- Query results during data loads
- Queries read many files while loads change table contents. Partial loads must remain invisible. Retries must follow the client's load identity.
- Concurrent workloads
- Reports can exhaust memory and shared data access. Separate compute workers alone cannot protect dashboard latency.
- Large analytical queries
- Scans, joins, and data skew require different execution plans. Worker failures can repeat work and corrupt results if the engine accepts duplicate output.
- Compute capacity changes
- Worker removal destroys caches and intermediate data. The service must preserve durable data and define what happens to active queries.
Common mistakes
- Tie durable table data to worker disks.
- Treat separate queues as complete workload isolation.
- Store every file reference in one catalog row.
- Expose files before the complete load commits.
- Repeat tasks without controlling duplicate output.
- Ignore the data bandwidth that the latency targets require.
The bar by level
- Senior (L5/E5)
- Defines snapshot capture, retry-safe load commits, and worker failure behavior. Explains join plans, memory limits, admission control, and safe pool suspension.
- Staff (L6+/E6+)
- Quantifies shared bandwidth and catalog limits. Defines isolation guarantees under overload. Covers concurrent commits, snapshot cleanup, capacity transitions, and cost trade-offs.