Distributed Systems

Designing a Distributed High-Throughput URL Shortener (Bitly / TinyURL)

Q: Should URL shorteners return HTTP 301 or 302 redirects?

Use 302 (Found / Temporary) if you need to track real-time click telemetry on every request. Use 301 (Moved Permanently) to allow browsers to cache redirects locally and reduce server load.

Q: Why is Base62 encoding preferred over MD5/SHA-256 hashing?

Cryptographic hashes produce long strings (32-64 chars) requiring truncation and complex collision handling. Base62 of a unique 64-bit ID guarantees zero collisions with exact 7-character length.

Senior / Staff

Design a high-availability URL shortening service capable of sub-10ms redirection latency using Base62 encoding, distributed unique ID generation (Twitter Snowflake), and multi-tier Redis caching.

Production Scale: 500M Links Created/Month • 100 Billion Redirects/Month • 100k QPS

Functional Requirements

•Generate unique 7-character short URL from long URL
•Redirect short URL (301 / 302 redirect) to long destination
•Custom aliases and click analytics

Non-Functional Requirements

•99.999% availability
•Ultra-low redirection latency (<10ms)
•Zero hash collisions

Capacity & Scale Estimation

New Short URLs500 Million / month (~200 writes/sec)

Redirection Queries (QPS)100 Billion / month (~40,000 reads/sec, 100k peak)

Read-to-Write Ratio200 : 1 (Heavily read-intensive)

Storage (5 Years)~15 Terabytes of URL mappings

Core Architectural Components

1Distributed ID Generator (Snowflake)

Generates 64-bit globally unique sequential IDs without database coordination using timestamp + worker ID + sequence bits.

2Base62 Encoding Module

Converts numeric 64-bit ID into a 7-character Base62 string (62^7 = 3.52 Trillion unique URLs).

3Multi-Tier Cache (Redis Cluster)

Caches the top 20% most frequently accessed URLs (80/20 rule) in RAM to serve 95%+ of redirects in <2ms.

4Distributed NoSQL / SQL Store

DynamoDB / PostgreSQL partitioned by ShortKey for permanent URL mapping persistence.

Architectural FAQs & Interview Deep Dives

Should URL shorteners return HTTP 301 or 302 redirects?

Use 302 (Found / Temporary) if you need to track real-time click telemetry on every request. Use 301 (Moved Permanently) to allow browsers to cache redirects locally and reduce server load.

Why is Base62 encoding preferred over MD5/SHA-256 hashing?

Cryptographic hashes produce long strings (32-64 chars) requiring truncation and complex collision handling. Base62 of a unique 64-bit ID guarantees zero collisions with exact 7-character length.