How the interviewer opens it
“Design a warehouse system that receives stock, assigns storage locations, and coordinates workers who pick and pack orders. Keep inventory accurate while workers perform tasks 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
- Warehouse scale
- Daily volume
- Request volume and mix
- Receipts and storage rules
- Order rules
- Latency
- Consistency and availability
- Workers and devices
- Durability and audit
- 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
- Receive known SKUs and assign compatible storage locations.
- Reserve stock for orders and assign pick tasks.
- Confirm physical moves and pack complete orders.
- Maintain accurate stock through concurrent work, retries, and reported discrepancies.
Usually out of scope
- Purchase plans and supplier payments.
- Carrier selection and shipment status.
- Robot control.
- Transfers between warehouses.
- Lot numbers, serial numbers, and expiry dates.
- Returns.
What interviewers ask about
- Stock for concurrent orders
- Several orders can request the last units while workers move stock. A server failure must not erase an accepted reservation.
- Locations for new stock
- Concurrent receipts can claim the same free space before either worker moves the goods.
- Work after device failures
- A worker can move goods before the server receives confirmation. A device failure can leave the stock location uncertain.
- Missing stock before pack confirmation
- A reservation does not prove that an item exists. A matching SKU in a tote does not prove that the order owns it.
Common mistakes
- Uses one inventory quantity without locations, reservations, or stock states.
- Checks stock or free space without an atomic claim.
- Omits links from pick tasks to allocations or from totes to orders.
- Subtracts the same stock during both the pick and the pack steps.
- Assumes a database transaction also guarantees the physical move.
- Promises no data loss without durable replication and safe failover.
The bar by level
- Senior (L5/E5)
- Defines quantity and capacity rules across each move. Links each pick to its exact allocation. Handles partial picks, deadlocks, stale confirmations, and missing stock. Defines durable commit acknowledgments and recovery after uncertain physical work.
- Staff (L6+/E6+)
- Defines authority for stock commitments, task ownership, and failover. Explains which replica can safely accept writes after failure. Uses scoped recovery and audit records to repair stock without a warehouse-wide stop. Explains which guarantees must change for offline work or orders across warehouses.