<aside> 💡 Solution

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Note: This document links directly to relevant areas found in the system design topics to avoid duplication. Refer to the linked content for general talking points, tradeoffs, and alternatives.

Step 1: Outline use cases and constraints

Gather requirements and scope the problem. Ask questions to clarify use cases and constraints. Discuss assumptions.

Without an interviewer to address clarifying questions, we'll define some use cases and constraints.

Use cases

We'll scope the problem to handle only the following use case

• Service calculates the past week's most popular products by category
• User views the past week's most popular products by category
• Service has high availability

Out of scope

• The general e-commerce site
  • Design components only for calculating sales rank

Constraints and assumptions

State assumptions

• Traffic is not evenly distributed
• Items can be in multiple categories
• Items cannot change categories
• There are no subcategories ie foo/bar/baz
• Results must be updated hourly
  • More popular products might need to be updated more frequently
• 10 million products