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This document is a system design of a URL shortening service for interview preparation. Steps in this document are following The complete guide to crack the System Design interview.
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URL shortening is to create shorter aliases for long URLs for better sharing, displaying and messaging.
For example, given URL of this document,
A shortened URL created by TinyURL is:
1. Requirement
Functional Requirement
Access a shortened URL
When users access to a short link, the service should redirect them to the original link if the short link is a correct one.
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Generate a shortened URL
Given any URL, the service should be able to generate a unique shortened URL, and short enough to be easily copied and share.
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The expiry for a short link
Links will expire after a default timespan.
Non-Functional Requirement
High availability
Consistency: eventual consistency
Latency: minimise latency when redirecting URLs
Reliability: No data loss
Others:
shortened links should not be predictable
2. Storage Estimation
Data Storage
Assumptions:
every shortened URL will be stored for 5 years
storage object will contain original url and shortened url, about 1,024 bytes
Storage:
1 million new URLs/month: 1 million * 12 * 5 * 1,024 bytes => 62 GB
10 million new URLs/month: 10 million * 12 * 5 * 1,024 bytes => 620 GB
100 million new URLs/month: 100 million * 12 * 5 * 1,024 bytes => 6.2 TB
Read Write ratio
This service will be read-heavy and assume read writer ratio as 100:1.
Number of requests to service
1 million new URLs/month:
read: 100 * 1 million = 100 million
for writing: 1 million / (3600 * 24 * 30) => 0.39 URLs/s
for reading: 100 * 0.39 = 39 URLs/s
10 million new URLs/month:
read: 100* 10 million = 1 billion
for writing: 10 million / (3600 * 24 * 30) => 3.9 URLs/s
for reading: 100 * 3.9 = 390 URLs/s
100 million new URLs/month:
read: 100 * 100 million = 10 billion
for writing: 100 million / (3600 * 24 * 30) => 39 URLs/s
for reading: 100 * 39 = 3900 URLs/s