Inventory Management

March 27, 2022 7:00 PM PDT

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This document summarizes the discussions and technical considerations regarding inventory management, specifically in the context of a system similar to Instacart. The focus is on functional and non-functional requirements, system design, and various technical challenges related to inventory management.

Meeting Details

• Topic: Inventory Management
• Level: L5 (Senior)
• Duration: 45 minutes
• Drawing Tool Used: Excalidraw

Requirements

Functional Requirements

• Manage inventory to prevent overshopping.
• Handle incoming shipments.
• Allow users to browse and add items to the cart while updating availability in real-time.
• Ensure no overselling of products.

Out of Scope

• Payment processing.
• Shipment logistics.
• Catalog management (handled by a neighboring team).

Non-Functional Requirements

• High availability.
• High throughput.
• Service reliability.

System Design

External APIs

• add_product(product, number): Adds a specified number of products to inventory.
• add_to_cart(user, product, number): Adds specified products to a user's cart.
• checkout(user, product, number): Processes the checkout for a user.

Database Design

• User Purchase Table

  • user_id
  • product_id
  • number
  • status (in_cart, bought)

• Product Table

  • product_id
  • sku_number
  • total_number

Service Logic

• The add_to_cart operation involves a database transaction that modifies two tables and commits the changes.
• Considerations for transaction management include potential issues with MySQL when handling large sizes.

Sharding and Transactions

• Discussed the challenges of sharding with MySQL and the need for distributed transactions.
• Proposed using an idempotent key for user actions to manage reservations and rollbacks effectively.
• Suggested using a cron job to ensure consistency between the idempotent key table and the product table.

Sharding Strategy

• Sharding can be based on product categories and names, but this may not be optimal for high-demand products.
• Caching strategies were discussed to improve performance.

Audience Feedback

• Emphasized the importance of managing inventory effectively, including handling abandoned carts and transaction consistency.
• Discussed the need for a clear understanding of data estimation and update granularity.
• Suggested exploring various solutions, including distributed transactions (2PC, SAGA) and in-memory databases.

Technical Discussions

• Differences between adding a new item versus adding a new product were clarified.
• The complexity of distributed transactions was acknowledged, with suggestions for using NoSQL solutions.
• Discussed the importance of cache strategies, including write-aside and write-through methods.
• Considered the implications of using RDBMS versus NoSQL for inventory management.

Conclusion

The meeting highlighted the complexities involved in designing an effective inventory management system. Key points included the need for robust transaction management, effective sharding strategies, and the importance of caching mechanisms to enhance performance. Further exploration of distributed transaction patterns and their implications on system design is recommended.