Design a device owner lookup service

Scenario

Your server receives a stream of events from clients. Each event contains:

• user_id
• device_id
• timestamp (event time)

A device may be associated with different users over time (e.g., shared device, logout/login, resale).

Core requirement

Build a backend service that supports:

• get_device_owner(device_id) -> user_id
  Returns the current owner of the device.

Assume “current owner” means the user_id from the latest event by timestamp for that device_id.

Constraints / concerns to address

• Events may arrive out of order .
• Clients may retry → duplicate events .
• Large scale (many devices; high write QPS; low-latency reads).
• Define behavior for ties (same timestamp) and missing devices.

Deliverables

• API design (ingestion + query)
• Data model
• Storage and indexing
• How you handle out-of-order/duplicate events
• Consistency guarantees and trade-offs
• Monitoring and operational considerations