Design a scalable inventory system
Overview
This question evaluates expertise in distributed systems and system design, focusing on real-time inventory management, concurrency control for reservations and oversell prevention, backorder handling, API and data model design, consistency models, and operational scalability.
Instacart
Aug 1, 2025, 12:00 AM
Software Engineer
Onsite
System Design
0
0
System Design: Scalable Inventory Management with Real-Time Stock, Reservations, Oversell Prevention, and Backorders
Context
You are designing the inventory subsystem for a large e-commerce marketplace with multiple fulfillment locations (warehouses/stores). Product availability must reflect real-time stock changes, support cart reservations, prevent overselling under high concurrency, and allow backorders when enabled.
Requirements
Design a system that:
- Maintains real-time stock across multiple warehouses/locations.
- Supports reservations for carts and orders (with TTL and conversion to order allocation).
- Prevents overselling under heavy concurrency.
- Supports backorders and allocation on replenishment.
- Exposes clear APIs (query, reserve, confirm, cancel, adjust, reconcile).
- Defines data models and storage choices.
- Specifies a consistency model with correctness guarantees and trade-offs.
- Outlines strategies for high availability, sharding/partitioning, and caching.
- Ensures idempotency and safe retries.
- Handles flash-sale spikes (hot SKUs) gracefully.
- Reconciles with external systems (suppliers/stores) and supports auditing/ledgering.
Provide architecture, key invariants, APIs, data schemas, and operational strategies addressing the above.
Solution
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