Can you design a URL shortening service like TinyURL?
This system design question asks candidates to architect a scalable web service for mapping long URLs to short identifiers. It covers database design, hashing, and load balancing.
Why Interviewers Ask This
System design interviews at Microsoft focus on scalability, reliability, and trade-offs. This question evaluates how well a candidate can handle high concurrency, generate unique keys, and ensure fast lookup times. It also tests knowledge of distributed systems concepts like sharding and caching strategies.
How to Answer This Question
Start by clarifying requirements such as read/write ratios and storage limits. Discuss generating unique IDs using Base62 encoding or consistent hashing. Explain the database schema for storing mappings. Address scaling challenges by mentioning horizontal partitioning or sharding. Finally, discuss caching layers like Redis to reduce database load for popular links.
Key Points to Cover
- Unique ID generation strategy
- Base62 encoding for compact representation
- Database sharding for horizontal scaling
- Caching for high read throughput
Sample Answer
To design a URL shortener, I would start by generating a unique ID for each long URL using a distributed ID generator or a hash function. This ID is then encoded into a shorter string using Base62 to maximize character usage. For storage, I would use a key-value store like Cassandra or DynamoDB, sharded by the ID prefix to distribute load. A caching layer using Redis would store frequently accessed mappings to minimize latency. To handle collisions, I would implement a retry mechanism or a larger key space.
Common Mistakes to Avoid
- Ignoring collision handling in hash functions
- Failing to consider global uniqueness across data centers
- Overlooking the need for a redirect cache
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