Social network - System Design

This repository describes the system design of social network within the course.

Requirements

The system should meet the following requirements:

Functional requirements

• Add and delete friends
• View users' friends
• View user's profile
• Publish posts
• View feed of posts (home and user feed)
• Upload media files for posts
• Send and read messages in one-on-one and group chats
• View one-on-one and group chats

Non-functional requirements

• 50 000 000 DAU
• Availability 99.99% (52.56 minutes downtime per year)
• The system should be scalable and efficient
• Each user sends an average of 1 post per 3 day
• Each user reads feeds an average of 10 times per day
• The size of each post is a maximum of 3000 characters
• The size of each media files is a maximum 1MB
• 10% of posts contain media files
• Each post has a maximum 3 media files
• A message should reach the recipient in 3 seconds
• Each user sends an average of 10 messages per day
• Each user reads messages an average of 20 times per day
• The size of each message is a maximum of 1000 characters
• A user can have a maximum of 1000 friends
• A group can have a maximum of 100 participants
• Posts and messages are stored forever
• Geo distribution is not supported (CIS only)
• No seasonality

Basic estimation

RPS

Send posts

$$ \frac{50 \space million}{(3 \space \times 24 \space hrs \times 3600 \space seconds)} = \sim 193 \space requests/second $$

Read posts

$$ \frac{50 \space million \times 10 \space times \space per \space day}{(24 \space hrs \times 3600 \space seconds)} = \sim 5787 \space requests/second $$

Send messages

$$ \frac{50 \space million \times 10 \space messages \space per \space day}{(24 \space hrs \times 3600 \space seconds)} = \sim 5787 \space requests/second $$

Read messages

$$ \frac{50 \space million \times 20 \space times \space per \space day}{(24 \space hrs \times 3600 \space seconds)} = \sim 11574 \space requests/second $$

Traffic

Send posts

Text traffic:

$$ {193 \space requests/second \times 2 \times 3000 \space bytes} = \sim 1.2 \space MB/second $$

Media files traffic:

$$ {193 \space requests/second \times 0.1 \times 3 \times 1 \space MB} = \sim 57.9 \space MB/second $$

Total:

$$ {1.2 \space MB/second + 57.9 \space MB/second} = 59.1 \space MB/second $$

Send messages

$$ {5787 \space requests/second \times 2 \times 1000 \space bytes} = \sim 11.6 \space MB/second $$

Storage

Database size for storing messages for 5 years:

$$ {11.6 \space MB/second \times (24 \space hrs \times 3600 \space seconds) \times 365 \space days \times 5 \space years} = \sim 1.83 \space PB $$

Database size for storing posts for 5 years:

$$ {59.1 \space MB/second \times (24 \space hrs \times 3600 \space seconds) \times 365 \space days \times 5 \space years} = \sim 9.32 \space PB $$

Total:

$$ {1.83 \space PB + 9.32 \space PB} = 11.15 \space PB $$

Number of disks (disk capacity = 16 TB):

$$ \frac{11.15 \space PB \times 1000}{16 \space TB} = \sim 697 \space number \space of \space disks $$

Design overview

Level 1. System context diagram

Level 2. Profile system container diagram

Level 2. Relation system container diagram

Level 2. Post system container diagram

Level 2. Media system container diagram

Level 2. Message system container diagram