You want to design a scalable rating and review system for millions of products and users. Which approach best balances fast average rating queries and frequent review updates?

hard📝 Trade-off Q15 of 15

LLD - Design — Food Delivery System

AStore all reviews and compute average on each query

BUse a single database table without indexes

CCache only the latest review per product

DMaintain precomputed average and count, update incrementally on review changes

Step-by-Step Solution

Solution:

Step 1: Consider query and update load
Millions of products and users mean many queries and updates.
Step 2: Choose efficient strategy
Precomputing average and count and updating them incrementally avoids scanning all reviews each time.
Step 3: Evaluate other options
Computing average on each query is slow; no indexes cause slow lookups; caching only latest review misses full rating info.
Final Answer:
Maintain precomputed average and count, update incrementally on review changes -> Option D
Quick Check:
Precompute + incremental update = scalable [OK]

Quick Trick: Precompute averages, update on changes for scale [OK]

Common Mistakes:

Recomputing averages on every query
Ignoring indexing and caching strategies
Caching incomplete data causing stale info

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More LLD Quizzes

You want to design a scalable rating and review system for millions of products and users. Which approach best balances fast average rating queries and frequent review updates?

Step 1: Consider query and update load

Step 2: Choose efficient strategy

Step 3: Evaluate other options

Final Answer:

Quick Check:

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