SWE Fundamental Concepts

🐸️ Introduction

In here I just wanted to share my personal note for fundamental concepts in SWE.

Interview Preparation

Answering Interview Questions

• Answer the question completely
• Share a relevant story from your past career
• Reference sample projects on GitHub that demonstrate your skills

Interview Process:

1. Resume/Application
   • Seek recommendations from friends or professional contacts
   • Network through coffee meetings or personal introductions
   • Leverage personal recommendations when possible
2. Coding Challenge
   • Prepare for various challenge types:
     • Data structure and algorithm problems
     • Multiple-choice questions
     • Domain-specific expertise
     • Demo app or feature development
   
   Best Practices:
   • Write clean, correct code
   • Break functions into small, focused units
   • Use a linter
   • Ensure clear problem understanding
   • Add comprehensive tests and comments
3. Recruiter Phone Screen
   • Approach as a friendly conversation
   • Discuss company culture and role
   • Be prepared to talk about salary expectations
   
   Key Tips:
   • Show genuine interest in the role and company
   • Read the company's blog
   • Maintain a balanced, professional tone
   • Ask engaging, thoughtful questions
4. Technical Screening
   • Expect questions on:
     • Data structures and algorithms
     • Method implementation
     • Past project discussions
   
   Preparation Strategies:
   • Deeply understand recent project challenges
   • Explain problem-solving approaches
   • Demonstrate language proficiency
   • Communicate clearly and confidently

💎️ Software Design Principles

Coupling and Cohesion

Cohesion

• Indicates the relationship within a module
• High cohesion is desirable
• All module items should be closely related
• Example: In a user class, all methods should relate to user functionality

Coupling

• Indicates relationships between software modules
• Low coupling is preferable
• High dependency between modules (e.g., user and post modules) suggests tight coupling

Software Requirements

Functional Requirements

• Specific end-user demands
• Basic facilities the system should offer
• Directly visible in the final product

Non-functional Requirements

• Quality constraints the system must satisfy

💎️ Processes and Threads

Process

• A program scheduled in the CPU
• Can create child processes
• Possible states: New, Ready, Running, Waiting, Terminated, Suspended

Thread

• A segment of a process
• A process can have multiple threads
• Three states: Running, Ready, Blocked

😈️ System Design Concepts

Scaling

• Vertical Scale: Adding RAM, CPU, and other resources
• Horizontal Scale: Creating multiple server instances

Key Distributed System Concepts

• Leader Election: Selecting a leader server with specific responsibilities
  • Examples: Zookeeper, etcd.io
• Logging: Recording system or software events
• Publish/Subscribe: Messaging pattern where publishers send messages without direct receiver specification
• Idempotent Operations: Operations that produce the same result regardless of how many times they're performed

💎️ Networking Fundamentals

Client-Server Model

• Client: Machine requesting or sending data to a server
• Server: Machine listening to and responding to client requests

DNS

• DNS Query: Request to obtain an IP address for a domain
• DNS Server: Translates domain names to IP addresses

IP Addresses

• Unique identifier for network-connected devices

IPv4 vs IPv6

Network Protocols

TCP (Transmission Control Protocol)

• Communication standard for packet transmission
• Ensures data integrity
• Establishes connection between source and destination

HTTP (Hypertext Transfer Protocol)

• Protocol built on TCP
• Request/response paradigm
• Uses port 80
• Versions:
  • HTTP/1: Basic implementation
  • HTTP/2: Server-push feature
  • HTTP/3: Parallel transmission streams

Network Layers

1. Application: HTTP, FTP, SSH, SMTP
2. Transport: UDP, TCP
3. Network (Internet): IP
4. Link (Hardware): WiFi, Ethernet
5. Physical: Physical cables

Protocol Characteristics

UDP (User Datagram Protocol)

• Lightweight (8-byte headers)
• Connectionless
• Inconsistent delivery
• Very fast
• Ideal for: Video games, video chats
• Unreliable transmission

TCP (Transmission Control Protocol)

• Connection-based
• Three-way handshake process
• Congestion control
• Reliable delivery
  • Delivery acknowledgments
  • Retransmission support
  • In-order packet guarantee

😈️ Performance and System Characteristics

Latency and Throughput

Latency

• Definition: Time taken for data to travel from one point to another
• Various types of latency:
  • Database read latency
  • Network latency (request round trip)

Latency Reduction Strategies

• Implement caching
• Improve database performance
• Optimize network infrastructure

Throughput

• Measurement of work performed in a specific time period
• Typically measured in:
  • GB per second
  • MB per second
• Indicates system capacity (e.g., server request handling)

😈️ System Availability

Availability Concepts

• System resilience and fault tolerance
• High Availability (HA)
• Service Level Agreement (SLA)

Availability Measurement: Nines

Improving System Availability

• Eliminate single points of failure
• Implement redundancy

Redundancy Types

• Passive Redundancy:
  • System continues operation if a component fails
  • Replication of failed parts
• Active Redundancy:
  • Remaining services automatically take over failed service duties

😈️ Caching and Performance Optimization

Caching Fundamentals

• Method of storing computation results
• Quick access without repeated computation
• Primary goal: System speed optimization

😈️ Proxy Technologies

Forward Proxy

• Server intermediary between client and server
• Client requests routed through proxy
• Source IP address modified
• Example: VPN services

Reverse Proxy

• Single entity for proxy and server
• Client perceives interaction with a single server
• Hides actual server infrastructure

😈️ Load Balancing

Load Balancer Strategies

• Distribute workloads across resources
• Request distribution methods:
  • Round-robin
  • Weighted resource allocation
  • Least-connection approach

Advanced Techniques

• Sticky-session cookies
• Ensuring consistent client-server routing
• Example: NGINX ip-hash directive

😈️ Hashing

• Transformation of arbitrary data to fixed-size value

😈️ Page Rendering Techniques

Server-Side Rendering (SSR)

• HTML rendering on client-side
• Improved SEO performance

Hydration Strategies

• Standard Hydration:
  • Attaching event handlers
  • Rendering on server and client
• Progressive Hydration:
  • Selective component hydration
• Resumability:
  • Dynamic JavaScript loading on user interaction

😈️ Database Technologies

Database Classification

Relational Databases

• Based on relational data model
• SQL (Structured Query Language) based

NoSQL Databases

• Flexible, scalable alternative to traditional databases
• No strict relational model

NoSQL Database Types

1. Key-Value Databases
   • Data stored as key-value pairs
   • Examples: Redis, Berkeley DB, Amazon DynamoDB
2. Document Databases
   • Data stored as documents (JSON/XML)
   • Examples: MongoDB, CouchDB, BaseX
3. Column-Oriented Databases
   • Data stored as strongly-typed columns
   • Quick aggregation of large data volumes
   • Examples: HBase, Bigtable, Cloudera
4. Graph Databases
   • Data stored in graph structures
   • Examples: Neo4J, InfiniteGraph

Database Selection Criteria

Choose SQL When:

• Highly structured, stable data
• Transactional requirements
• Complex query needs

Choose NoSQL When:

• Large data volumes
• Dynamic schema flexibility
• Horizontal scalability requirements

Database Characteristics

ACID Properties

• Atomicity: Complete or no transaction
• Consistency: Maintain data integrity
• Isolation: Prevent transaction interference
• Durability: Committed transactions survive system failures

Specialized Database Types

• Blob Storage: Unstructured data storage
  • Examples: Google Cloud Storage, S3, Minio
• Time Series DB: Event and time-relevant data
  • Examples: InfluxDB, Prometheus
  • Use cases: IoT, logging, monitoring
• Spatial DB: Geographic and spatial data storage

Data Management Strategies

Replication

• Multiple database node synchronization
• Benefits:
  • Increased read performance
  • Fault tolerance
  • Asynchronous data writing

Sharding

• Data distribution across multiple servers
• Types:
  • Vertical sharding: Column distribution
  • Horizontal sharding: Row distribution
• Requires middleware for operation routing

😈️ Distributed Computing

MapReduce Framework

• Large dataset processing across multiple servers
• Two-phase processing:
  • Map: Data splitting and key/value mapping
  • Reduce: Data shuffling and reduction

😈️ Encryption Techniques

Symmetric Encryption

• Single key encryption
• Examples: AES, Triple DES
• Advanced Encryption Standard (AES)

Asymmetric Encryption

• Two-key system (public/private)
• Public key: Encryption
• Private key: Decryption
• Digital signature generation via message hash encryption