aakhtar3

Posted on Mar 26, 2023 • Updated on Mar 18

System Design

#architecture #computerscience #systems #tutorial

A high level break down of key components when doing a system design problem.

Requirements	Estimations	Network	Application	Database
Functional	Calculations	WAN	Load Balancer	SQL
Non-Functional	QPS	Payload	Service Discovery	NoSQL
Architecture	Max QPS	Gateway	Consensus	CAP PACELC
Key Performance Indicators	Storage Bytes	VPC	Compute	Partition
-	Retention Bytes	-	Message Queue	Index
-	In E Gress Bytes	-	Cache	ACID

Requirements

Get requirements and estimations to scope your system design.

Functional

Identity what you are trying to build.

Features	System
1 on 1 chat	Mobile/Web
News feed	Notifications

Non Functional

Identify how your system will behave.

User Experience	System
Full end to end encryption	High Availability
See new post fast	Reliability

Architecture

High Availability
Failover

Reliability
RPO/RTO

Key Performance Indicators

Observability
Metrics

Estimations

Value	Number	Byte
Hundred	-	B
Thousand	K	KB
Million	M	MB
Billion	B	GB
Trillion	T	TB
Quadrillion	Q	PB
Quintillion	Qu	EB
Sextillion	S	ZB
Septillion	Se	YB

Estimate the scope of your users and data points.

Users (DAU)	File Type (File Bytes)	Storage (Retention Time)
100 B Message/day	1 KB (avg)	10 years
10 B Post/day	10 KB (max)	10% new data per year

Calculations

Using your estimations do some back of envelope.

QPS	Max QPS	Storage-Bytes	Retention Bytes	In/E Gress Bytes
DAU / ~100K	2 * QPS	DAU * FileBytes	StorageBytes * Retention Time	(QPS * FileBytes) / 8 Bit

QPS

Queries Per Second
Daily Active Users
Time = Round up (86,400 seconds in day)

Max QPS

Double Queries Per Second
Calculate (Read % : Write %) Ratio
- 1 Read : 10 Write
- Read % = 1 * Queries Per Second
- Write % = 10 * Queries Per Second

Storage Bytes

Storage Bytes
Daily Active Users
File Bytes

Retention Bytes

Retention Bytes
Storage Bytes
Retention Time
- 365 days in year

In E Gress Bytes

In-gress
E-gress
1 Byte / 8 Bits
Queries Per Second
File Bytes

Network

Wide Area Network

Clients
- Mobile
- Browser
- CLI
DNS
- DNSSec (Signed Registries)
- DNS over HTTPS (Privacy)
CDN
APN

Payload

API
Request Lines
Authentication/Authorization
Protocols

Public Gateway

Firewall
Rate Limiter
Authentication/Authorization
Reverse Proxy
Forward Proxy

Virtual Private Cloud

Access Control List
Security Group
Route Table
Classless Inter-Domain Routing
Gateway
- Internet
- Network Adress Translation
- VPC Peering

Application

Load Balancer

Layer 3/4/7 OSI
Strategy
Use cases

Service Discovery

Auto Scale
- DevOps
Protocols
Zeekeeper/etcd

Consensus

Raft Consensus
Replicated State Machine

Compute

Session(less)
State(full)/(less)
Server(less)

Message Queue

Producer
Consumer

Cache

Eviction Strategy

Database

SQL

Relational Data
Transactions

NoSQL

Key Value
Document
Wide Column
Graph
TimeSeries
Spatial

CAP PACELC

CAP
- Consistency
- Availability
- Partition
PACELC
- Partition == true
  - IF
- Availability
  - or
- Consistency
  - ELSE
- Latency
  - or
- Consistency

Partition

Consistent Hashing
Range Partition
Vertical Partition

Index

B Tree
Skip List
Hash
Inverted

ACID

Atomicity

Transactions
Rollbacks

Consistency

SQL Consistency

Schema
Constraint
Fan Trap

NoSQL Consistency

Eventual Consistency
Sequential Consistency
Strong Consistency

Strong Eventual Consistency
Quorum Replication
(Dotted) Vector Clocks
Chain Replication

Isolation

Race Conditions
Lock
Concurrency

Durability

High Watermark
Checkpoint
Write Ahead Log