estudy.

estudy. #

This estudy repository is a collection of records I wrote while researching and studying the discipline of software. From simple theoretical notes to deep dives and research, personal thoughts and appeals, and values and experiences I consider important are also contained here. Lately, I've been conceiving the concept of a "developer's fast lane," and I'm asking myself if recording (記錄) can break the commandments of scale and entry.

Of course, if the act of recording itself were merely a means to show off to someone or satisfy intellectual vanity, I wouldn't have created this repository. However, as trees are planted to some extent, and I see the forest gradually taking shape, it feels as if my hidden desires are being revealed. There are times I want to write something I'm proud of, and I also write because I find intrinsic value in the act of recording itself.

Whether the motivation is internal or external, one thing is certain: the data of these records themselves become eternal the moment they are committed here, and regardless of whether the content, structure, or format differs, everything in this repository is precious and valuable data. The introduction has become long. In any case, this repository is simply a collection of records with various values as a software developer. Some content might not be helpful to you, but I hope some might become a turning point.

"I sincerely welcome and thank you for visiting estudy, my forest of knowledge."

Essentials #

• Growing as a Software Engineer
• Why do seniors tell us to print Hello World?
• YAGNI (You Ain't Gonna Need It)
• Agile Software Development
• Definition of Doing Work Well vs. Developing Well
• Enhancing My Competency: A Path to Sustainable Growth
• Carpe diem
• How to Survive in the AI Era

Server #

• KISS, YAGNI, DRY
• Authentication vs. Authorization
• Efficient Design Methods for Back-end API Documentation
• Java Backend Web Technology History
• Clean Architecture with Spring Boot
• ☁️ Understanding OAuth 2.0 Concepts and Grant Types
• 3rd Karrot SRE Meetup
• Checking Test Coverage in IntelliJ
• SOLID Principles and the Pros and Cons of Each
• Differences in the Directions Kotlin and JPA Pursue
• Netty
  • Java IO, NIO
  • Java NIO - Selector
  • 비동기식 이벤트 기반 네트워킹
  • 네티의 핵심 컴포넌트
  • Netty Thread Model
• Netty Message Flow
• Netty Thread Model, EventLoop
• ByteBuf, Memory Management
• Mechanism by which Netty identifies completed tasks
• Netty Async Flow Control
• EventLoopGroup
• NioEventLoop vs EpollEventLoop
• Netty Native Memory Tuning, BackPressure
• Reactive Programming: What You Need to Know
• Elegant Spring Batch by Woowa Bros. Lee Dong-wook
• Cache Eviction, Expiration, Passivation
• Protocol Buffers
• Redis 분산락 + WebFlux 프로젝트
• Apache Kafka Key Components: Producer, Consumer, Topic, Partition, Segment
  • Apache Kafka Key Components 2: Zookeeper, Broker + Clustering Walkthrough
• Understanding the PUB/SUB (Publish/Subscribe) Architecture
• Kafka Rebalancing
• Kafka Consumer Offset Manual Commit
• Kafka ISR(In Sync Replica)
• Producer Key Options
• Kafka Disk I/O
• How Kafka Replication Works
• Kafka Partition Assignment Strategies
• State Machine
  • Kafka Partition
• State Machine Pattern
• How are sessions shared and managed in a multi-environment?
• Distributed Consensus Algorithm Paxos
• Kernel
  • Block IO (Buffer Head, BIO Struct, Scheduler)
• Linux
  • Command nmap
• LXC (Linux Container)
• Linux Performance analysis commands
  • uptime
  • dmesg
  • free
  • df
  • top
  • netstat
  • epoll
• Linux File System
• Kernel Space vs User Space
• System Call Interface
• buffer_head
• Time Synchronization Issues in Distributed Systems
• Distributed System Logical Clocks (Lamport Clock, Vector Clock)
• Implementing DR with IDC Redundancy + Kafka
• Data Partitioning
• What is MSA Microservice Architecture?
• Microservices from the Perspective of the Scaling Cube
• MSA, MA, SOA(Service Oriented Architecture), ESB, SOAP
• Reasons Not to Use DNS and Load Balancer for Service Discovery
• Microservice Client Resilience Patterns
• MSA 핵심 디자인 패턴
  • Two Phase Commit
• Saga Pattern
• Event Sourcing
• CQRS
• Transactional Outbox Pattern
• Microservice Architecture IPC
  • Synchronous RPI Pattern Application Communication
• 서비스 디스커버리 Service Discovery
• Asynchronous Message Pattern Application Communication
• Service Mesh
• Istio, Istio Architecture
  • Envoy Proxy Internal Architecture
• xDS Protocol, Control Plane (Istio Pilot)
• Traffic Control & Security mTLS
• Istio Circuit Breaker
• Managing Distributed Transactions in Microservices
• SRE
  • SLO, SLI, SLA
• Socket Programming
• Encryption Algorithm AES256
• Low Level, JVM Async Programming
• Data-Driven Thinking (Observability + Capacity Planning)
• Failover Consistency
• Netty Proxy
• TCP Syn, Accept Queue
• Handling Resource Constraints of External Integration Systems and Surging Traffic
• 성능 테스트
• WAL, Distributed System Data Consistency, and Disaster Recovery Patterns
• Cache System Design
• Cache System Design and Implementation
• Cache Zero-Downtime Migration (Lazy Migration)
• Identifying Failure Points and Designing C/A Systems
• When a master node goes down after acquiring a distributed lock
• Controlling Cache Stampede (Distributed Lock, PER)
• Large-Scale DB and Data Migration (DB & Storage)
• Resolving SNAT Port Exhaustion and DNS Resolution Latency Issues
• Handling Duplicate Messages and Ensuring Idempotency During Kafka Partition Rebalancing
• Distributed Consensus Algorithms
• Why Zookeeper Adopted Paxos

DevOps #

• DevOps Engineer
• Docker and Kubernetes
• Differences between IaaS, PaaS, and SaaS
• CI/CD Pipeline and Implementation Process
• Virtual Machine vs. Container
• Types of Deployment Strategies (Rolling/Blue-Green/Canary)
• Docker Container
  • Container Control Commands
• Container Management Commands
• Image-Related Commands
• Let's Spin Up a Docker Container
• Exposing Containers Externally
• Building Container Applications
• Using Docker Volumes
• Docker Network Structure
• Container Logging
• Container Resource Limits
• Creating a Docker Image
• Docker Swarm
• Deploying a Spring Project Using Docker
• permission denied while trying .. Docker demon socket Troubleshooting
• Docker Engine LXC, libcontainer
• Namespace, Container + runc syscall tracking
• Kubernetes
  • Desired State
• Kubernetes Components
• Kubernetes API Resources
• Kubernetes Operation Flow
• Kubernetes Dashboard Token Issuance and Access
• Kubernetes Cluster
• Control Plane
• Pod
• Pod LifeCycle(Phase, Condition)
• Pod Lifecycle, Restart Policy
• Multi-Container Pod Design Patterns
• QoS Classes
• Node Scheduling
• Probe
• Service - Cluster IP, Node Port, Load Balancer
• Service - Headless, Endpoint, ExternalName
• ReplicaSet
• Deployment
• DaemonSet, Job, CronJob
• Volume - emptyDir, hostPath, PV/PVC
• ConfigMap, Secret
• Namespace, ResourceQuota, LimitRange
• Cluster Autoscaler, Karpenter
• Scheduler, Controller
• PV/PVC, Dynamic Provisioning
• Kubernetes Network
• K8s RBAC, Security Policy
• Agile Methodology
  • K8s Deployment Strategies, Probes
• Cloud Architecture
  • Node Components
• Hybrid Cloud
• Testing
• Walkthrough, Inspection
• What is TDD (Test-Driven Development)
• GitHub Actions
• Basic Concepts of Cloud and AWS
  • What is Amazon Web Service EC2
• EC2 Pricing Policies and Instance Types
• EBS, Instance Storage, AMI
• AWS Security Group
• AWS ELB (Elastic Load Balancer), Sticky Session
• Auto Scaling
• VPC
• NAT, NAPT, and AWS NAT Gateway
• AWS Routing Tables
• Difference Between High Availability and Fault Tolerance
• AWS RDS (Relational Database Service)
• Elastic IP
• Systems Manager Session Manager
• Amazon Aurora, Aurora Architecture
• AWS Aurora 2nd
• CloudWatch vs CloudTrail
• SES Simple Email Service
• SNS SImple Notification Service
• SQS
• Optimization Improvements for Amazon SQS Speed and Scaling
• CloudFront
• AWS ECR (Elastic Container Registry)
• AWS ELK (Elastic Search Logstash Kibana)
• How to Access Private EC2 via Bastion Server + Hi-v2 Troubleshooting
• CloudWatch
• EKS
  • EKS CNI
• Pod Communication Process
• EKS ALB Controller
• Creating and Deleting NLB and ALB
• Site to Site VPN
• DX (Direct Connect)
• Monolithic Architecture
• APM (Application Performance Management)
• gRPC, RPC, How It Works, HTTP API Comparison
• RabbitMQ
• Blue/Green Deployment and Architecture
• Nginx
• ELK and Logging Configuration
• Prometheus, Grafana
• Prometheus Exporter - Monitoring Agent
• Blue/Green Deployment, Auto Scaling
• Server Redundancy Architecture
• GitOps
• HCL Language
  • [Terraform] EKS 배포 프로젝트
• Terraform Custom Condition(precondition, postcondition)
  • How Terraform Works
• Terraform dynamic block
• [Terraform] state, remote_state, backend
• MicroService Monitoring System (cc. Loki/Grafana)
• Presto
• Service Discovery Patterns in MSA
• IAM (Identity and Access Management)

SRE #

• Parallel GC Hang Alert
• Main Causes of Pod Pending Status
• kube-proxy Role
• Differences between iptables and ipvs
• CNI (Container Network Interface)
• Pod to Pod Cross-Node Packet Flow
• HPA (Horizontal Pod Autoscaler) Operation Principle
• Potential Risks When Using VPA
• Necessity of PDB (Pod Disruption Budget)
• Node Pressure (OOM, DiskPressure)
• Classifying CrashLoopBackOff Causes
• Comparing StatefulSet and Deployment
• Ingress vs. Service
• Pod Management Process in kubelet
• Liveness, Readiness, Startup Probe Comparison
• The Role of containerd
• How OOM Killer Works
• Why epoll is More Efficient Than select/poll
• Interpreting CPU Load Average
• CPU and Memory Control Methods in cgroup
• Symptoms of File Descriptor Exhaustion
• Causes of TCP TIME_WAIT Increase
• Causes of DNS Lookup Timeout
• Why Using Swap Is Dangerous
• Performance Issues Arising from NUMA Architecture
• Thread Pool Size Calculation Principles
• Advantages of Prometheus's Pull Model
• Alertmanager's Role
• p95·p99 Latency Difference Analysis
• The Dangers of High Cardinality
• Necessity of Filtering in Log Collection Systems
• Role of Jaeger and Tempo
• OpenTelemetry Structure
• Comparing SLO and SLI
• Symptoms of MTU Mismatch
• The Danger of Retry Thundering Herd
• Connection Pool Exhaustion Symptoms
• Nginx 502·504 Difference
• How to Detect Slow Queries
• Causes of Thread Overflow
• Root Causes of Increased GC Pause
• Priority Judgment Criteria During Outage Response
• Incident Severity Calculation Method
• How to Establish a Rollback Strategy
• Blue/Green Deployment vs Canary Deployment
• How to Configure DNS Failover
• How to Write Post-Mortem Action Items (Including Runbooks)
• Incident Flow: Detection → Triage → Mitigation → RCA
• Alert Fatigue Reduction Strategies
• Stability Checks to Consider for Deployment Automation
• Applying SLA and Error Budget

Languages #

• Java
  • Object-Oriented
• JVM Memory Structure
• JMM (Java Memory Model)
• JVM Memory Model
• JVM GC
• Types of GCs and Their Differences
• Four Types of Garbage Collectors
• G1GC
• Java String Pool
• 4 Characteristics of OOP
• 5 Object-Oriented Principles
• Class, Object, Instance
• Constructors and Initialization
• Overriding and Overloading
• Polymorphism
• Date, SimpleDateFormat Current Date, Time Output
• Collection Framework
• Exception Handling
• RuntimeException and Exception
• HashMap Methods and Usage
• Understanding Optional
• What is a Web Servlet?
• StringBuilder Usage and Key Methods
• Wrapper Class, Boxing and Unboxing
• Java Generic
• SocketAddress Class & NetworkInterface Class
• Java String, StringBuilder, StringBuffer 차이 알아보기
• 🧐 Understanding POJO (Plain Old Java Object)
• Java Reflection
• Java Executors
• Java Callable, Future
• Java Cleaner, PhantomReference class
• How to Resolve OutOfMemoryError
• Java's Four Reference Types (Strong, Weak, Soft, Phantom)
• Java 8 Functional Interface
• Built-in Functional Interfaces in Java
• Reactive Stream, Backpressure, API Components
• Cold Publisher & Hot Publisher
• Java AIO
• JDK Proxy, CGLib Proxy
• Hotspot VM, JIT Compiler, and Their Limitations
• GraalVM
• Native Image
• Memory Optimization for Native Images
• Java Exception Creation Cost, and How to Reduce It
• JVM Warm Up - Causes of Latency Degradation Immediately After Deployment
• Applying JVM Warm Up
• ReentrantLock, Condition
• JIT Compiler
• Native Memroy
• jemalloc
• jemalloc, arena, memory fragmentation
• JVM Heap Object Headers on Internals
• JVM Safepoint
• Bias Locking, Revocation
• CAS (Compare And Swap)
• vDSO(virtual Dynamic Shared Object)
• Object Header - Mark Word
• GC Write Barrier
• Card Table
• Incremental Update
• Parallel GC Tuning
• CMS GC (Tuning Strategy: Parallel, CMS)
• G1GC
  • Evacuation Failure
• Why did G1GC choose SATB instead of Incremental Update?
• Mixed GC
• Concurrent Marking
• G1GC OpenJDK 8 and 11
• Humongous Object, Mixed GC Trigger
• ZGC (Z Garbage Collector)
  • G1GC, ZGC Performance Comparison Test
• Marked0/1, Good/Bad Color
• Parallel GC to G1GC
• TLAB (Thread-Local Allocation Buffer)
• Safepoint and Polling Page
• Reactive Streams
• HotSpot JVM ZGC Barriers, NUMA Memory Allocation, and Safepoint Operations
• Object Lifecycle (Creation, Usage, Destruction)
• Methods of Java's Object Class
• PGO (Profile-Guided Optimization)
• What is the role of the Finalize method in Java?
• Devirtualization: Polymorphism Implemented by the JVM
• Abstract Methods and Abstract Classes
• 5 JVM Method Invocation Instructions
• JMM and Hardware Intersection
• Anatomy of JVM Observability Tool Principles
• JIT Compiler, GraalVM: Java Code to Machine Code Translation Process
  • Kotlin DSL
• Creating Pair Instances with mapOf() and to
• Kotlin Object-Oriented Programming
• Functional Programming in Kotlin
• Kotlin Collections
• Kotlin Delegates
  • 고차 함수 (High-order-function)
• Kotlin Scope Functions
• Kotlin Sequences and Lazy Evaluation
• Kotlin Functional Interfaces and SAM Constructors
• [Kotlin] What is kapt?
• Why can't the Lombok library be used in Kotlin?
• Using Spring Framework with Kotlin
• Implementing Persistence with Data Classes
• @JvmField && @JvmStatic Annotations
• Writing Test Code with Kotest
• Kotlin Coroutines and Concurrency Programming
• My Favorite Kotlin companion object
• Kotlin Generics: Covariance, Contravariance, Invariance
• Kotlin Generics Star Projection, reified Types
• sortedWith, Comparator Sorting Lambda Expression
• Kotlin runCatching and Result Type
• Differences between Unit and Nothing in Kotlin
• How to Create a Singleton Class in Kotlin?
• What is the difference between companion object and object?
• Functions Outside a Class (A package-level/ Top-level function)
• Kotlin Class, Field vs Property
• Reducing Coupling with Kotlin Delegation
• Proper Null Handling with lateinit and Delegates.notNull<>()
• Efficiently using use when working with classes that require .close()
• infix, inline function
• sealed class
• Optimize Higher-Order Functions Using inline fun
• Coroutine
• What is Kotlin and Why Do We Need It?
  • CoroutineDispatcher
• launch, async
• suspend fun
• Making Coroutine Jobs Lazy
• Coroutine Job State Management
• Coroutine State Variables
• CoroutineContext
• Golang
  • Understanding Handle, Handler, and HandleFunc
• Pointers and Dereferencing in Golang
• Using Sqlite3 with Go Databases
• REST API Server using gorilla/mux
• JavaScript
  • Function
• Basic Js
• Prototype
• Garbage Collection
• Object Methods
• Class
• Strings
• Math
• Array
• Array 2
• Data Immutability
• Destructuring Assignment
• export
• import
• Lodash
• JSON
• Storage
• Regular Expressions
• DOM API
• Frequently Used DOM API Summary
• Promise
• AJAX
• fetch API
• TypeScript
  • Class
• Type
• Constructor, Access Modifiers, Getter and Setter
• Functions in TypeScript
  • 작성자와 사용자의 관점으로 코드 바라보기
  • Structural Type System vs Nominal Type System
  • 타입 호환성 Type Compatibility
  • 타입 별칭 Type Alias
  • TypeScript_Compiler
  • constructor, Access Modifier, Getter & Setter
• Interface
• Interface2
  • 클래스 (class)
• Generic
• Component

Frameworks #

• Node.js
• Npm(Node.js) - Basic Command Usage Summary
• What is the MVC Pattern?
  • React
• Controller, Service, Repository
  • TypeScript Compiler
• IoC Container (Inversion of Control)
  • conflict - Resolving Conflicts
• What is a Spring Bean?
  • git log - Check History
• Spring AOP (Aspect Oriented Programming) Concepts
  • git Basic Commands Summary 2
• Spring AOP Library AspectJ
  • Creating package.json
• Spring's Representative @Annotations and Their Roles
  • pull request
• What is Spring JDBC, DataSource?
  • version
• Spring Package Structure - Layered vs. Domain-Driven
  • Other Commands
• Lombok: A Collection of @Annotations You Must Know
  • GitHub Terminology
• About Spring Boot @Builder
  • Managing Someone Else's Repo
• Spring/Spring URL Mapping
  • Branch
• Spring Security AccessToken & RefreshToken
  • Building a Server
• Log Management Every Developer Must Do: Slf4j Logger
  • Remote Repository
• Understanding Jwt (Json Web Token)
  • Reverting to a previous version,
• Validation using Spring Validation
  • Class Components
• Spring Boot Exception Handling with @ExceptionHandler
  • Package Installation / Uninstallation Commands
• (Spring boot + Security) Configuring SecurityConfig
  • Functional Components
• Automating API Documentation with Swagger
• [Spring] Let's fully understand IoC, DI, Spring Container, and Bean 📗
• 🌱 [Spring] What exactly is AOP (Aspect-Oriented Programming)? 🧐
• 💻 Understanding the Concept and Operation of Dispatcher-Servlet
• 🔒 Understanding the Characteristics and Differences Between Servlet Filter and Spring Interceptor
• [Kotlin, Spring boot] copy() Deep Copy, Shallow Copy Performance Benefits? 🤔
• [Kotlin, Spring boot] Data Processing Efficiency in Search API: find Query vs. Internal Function? 🤔
• 📗 Spring Boot Actuator API + Example using Spring Cloud
• 📗 Mastering Spring WebFlux, Reactive Stream, R2DBC, Mono, Flux
• Springboot에서 데이터베이스 인덱싱 하는 방법
• Annotations for Spring Security Authentication in Spring Tests
• Connection Pool in Spring, HikariCP
• Spring Boot Batch
• Is ControllerAdvice implemented with AOP? Let's look at its operation.
• How ObjectMapper Works and Additional Features Provided by Spring Boot
• Kotlin Test Framework mockk Usage
• Spring Data Binding, Converter, Formatter
• Spring Resource Interface, Resource Abstraction and Implementations
• ResourceLoader, ResourcePatternResolver, ApplicationContext and Resources Paths
• SecurityContextHolderStrategy (ThreadLocal, InheritableThreadLocal, Global)
• Spring Security Filter
• Difference between Mock and Stub Tests
• Plugins and Dependencies for Running Spring in Kotlin
• Spring Boot Embedded Web Server Tomcat Configuration, How to Configure Other Embedded Web Servers
• Flexible Parameter Handling with Spring ArgumentResolver
• Perform actions periodically using Spring Scheduler
• Configuring Spring Boot Project Profiles
• Bean Scope, DL(Dependency Lookup), Provider
• JDBC, DriverManager
• Separating Transactions Using Spring AOP and Dynamic Proxies
• Application Logic, Infrastructure Beans, Container Infrastructure Beans
• Bean Scopes, Potential Issues, and Solutions
• Spring WebFlux vs MVC, Internal Working Principles
• Spring Batch Technical Trade-offs
• Spring Batch Data Consistency Management
• Spring Data JPA and @Transactional
• How Spring Data JPA Works
• How to Control Spring AOP Advice Order
• Spring Data JPA @Modifiying
• High Hibernate Performance, NaturalId
• JPA Entity equals(), hashcode() overriding
• Persistence Context
• Flush
• Object and Table Mapping
• Automatic Database Schema Generation
• Hibernate
• Embedded Types @Embedded, @Embeddable
• How to find an object by FK using the @Query annotation
• JPA N+1 Problem Resolution Methods and Practical Application Tips
• Differences Between Regular Join and Fetch Join
• When to Use a Regular Join?
• JPA Propagation Transaction Propagation Steps
• JPA Proxy and Lazy Loading
• OSIV (Open Session In View)
• Bulk Update, Delete Operations and the Persistence Context
• Spring @Transactional Transaction Binding and Auto-Commit

Domain Driven Design #

• 🔨 DDD (Domain-Driven Design) and Domain Model
• [Domain-Driven-Design] Bounded-Context ✍️
• [DDD] Understanding Domain-Driven Design Aggregates
• Application Service and Presentation Layer
• Features Requiring Multiple Aggregates and Domain Services
• Aggregate and Transaction Management
• Domain Model and Bounded Context
• Event - High Coupling Issue Between Systems
• Events, Handlers, Dispatchers
• Synchronous Event Processing Issues, Asynchronous Event Processing
• CQRS (Command Query Responsibility Segregation)

DataBase #

• 데이터베이스
• Database
• Database 2
• SQL Basic Syntax Summary
• DDL (Data Definition Language)
• Concept and Types of Keys
• ORM Concepts, Types, and Application Methods
• 트랜잭션과 ACID
• Database Normalization
• Index and Its Working Principle for Database Performance
• Replication vs Clustering
• Database Sharding (Distributed Processing)
• CAP Theorem
• Data Modeling and Types of DBs Based on Data Characteristics
• Database Connection Pool
• Database Optimizer
• Optimizer Optimization, Goals, and Limitations
• Cluster and Conditions in Databases
• Clustering (Active Clustering, Standby Clustering)
• SQLD
  • Entity, Attribute, Relation
• Identifier Types and Classification System
• Database Normalization
• Denormalization
• DDL (CREATE, ALTER, DROP, TRUNCATE) Practice
• DML (INSERT, UPDATE, DELETE, SELECT) Practice + TCL (COMMIT, ROLLBACK)
• DCL (GRANT, REVOKE) Practice, User Creation
• WHERE Clause Practice
• Practicing Data Sorting with ORDER BY
• GROUP BY, Practice Data Aggregation by Group with Aggregate Functions
• Summary of Join Operations
• INNER JOIN & OUTER JOIN Practice
• Practice Using SQL DATE Functions + DUAL Table
• Practice Modifying Data with REPLACE() Function
• Practice Truncating Character Data Using the SUBSTR() Function
• Case Sensitivity Practice Using UPPER() and LOWER() Functions
• Numeric Functions ROUND(), TRUNC(), CEIL() Practice
• SQL Window Functions (WINDOW FUNCTION)
• Hierarchical Queries (START WITH, CONNECT BY PRIOR, SIBLINGS BY)
• SQL NULL-Related Functions - NVL, NVL2, NULLIF, COALESCE
• Differences Between Procedures and Triggers
• SQL vs NoSQL
• MongoDB
  • Document Database
• MongoDB Trade-offs (vs RDB)
• MongoDB - CRUD
• MongoDB Sharding
• MongoDB Data Recovery (UNDO, REDO)
• Redis
  • Efficient Redis Server Configuration
• Redis Memory Management, Optimization Strategies
• Redis Fragmentation Ratio
• Redis Distributed Lock, RedLock
• Redis Cluster
• Redis Distributed Lock, Example Spring Boot
• How to Ensure Atomicity for Multiple Redis Commands
• Redis Architecture
• Redis Replication
• How to Prevent Data Loss During Redis Failover
• Redis important fact about replication
• Redis INCR
• Redis Serialization Sync
• Database Load Balancing (Partitioning, Sharding, Replication)
• 데이터베이스 파티셔닝
• 파티셔닝 종류와 분할 기준
• VARCHAR vs TEXT
• Serializability
• Recoverability
• Full-Text Search Index
• Covering Index
• MMR, BKA
• MySQL 8.0 InnoDB Locking
• Pessimistic Lock, Optimistic Lock
• LSM Tree
• B+Tree
• Improving LIKE Query Search Performance, Full-Text Search
• Improving Query Performance with Analytic Functions
• Deadlock
• MySQL MyISAM, InnoDB
• MySQL WAL
• InfluxDB

Design Pattern #

• Design Patterns
  • 생성 패턴
    • Singleton Pattern
• Factory Method Pattern
• Abstract Factory Pattern
• Builder Pattern
• Prototype Pattern
  • 행동 패턴
• Template Method Pattern
• Observer Pattern
• Strategy Pattern
• Singleton Pattern
• State Pattern
• Chain of Responsibility Pattern
• Command Pattern
• Interpreter Pattern
• Iterator Pattern
• Mediator Pattern
  • 구조 패턴
• Proxy Pattern
• Adapter Pattern
• Composite Pattern
• Decorator Pattern
• Facade Pattern
• Bridge Pattern

Network #

• 인터넷 네트워크
• IP (Internet Protocol)
• TCP & UDP
• PORT & DNS
• URI와 웹 브라우저 요청 흐름
• URI
• Web Browser Request Flow
• HTTP 기본
• Everything is HTTP
• Client-Server Architecture
• Stateful, Stateless
• HTTP Messages
• HTTP 메서드, 활용
• Connectionless
• Let's Create an HTTP API
• HTTP Methods - GET, POST
• PUT, PATCH , DELETE
• Properties of HTTP Methods
• Client to Server Data Transfer
• HTTP API Design Examples
• HTTP 상태코드
• HTTP Status Codes
• 2xx - Success
• 3xx - Redirection
• 4xx - Client Errors, 5xx - Server Errors
• HTTP 헤더 - 일반 헤더
• HTTP Header Overview
• Negotiation, Transfer Methods
• General Information
• Authentication, Cookies
• HTTP 헤더 - 캐시와 조건부 요청
• Cache Basic Operation
• Validation Headers and Conditional Requests
• Cache and Conditional Request Headers
• Proxy Cache
• Network
• Network Protocols
• How the Internet Works
• HTTP
• How DNS Works
• Domain Name
• How Web Browsers Work
• Hosting
• Synchronization and Deadlock
• Meaning and Design Rules of RESTful API
• Protocols by Network Layer
• Apache Tomcat (Apache Tomcat)
• Network Web Communication Flow
• Web Cache (Proxy Server)
• CDN (Content Delivery Networks)
• P2P
• Switches and Routers, Switching and Routing
• Inbound, Outbound
• Circuit Switching and Packet Switching
• IP/IP Packet, Packet Delivery, Limitations
• OSI 7 Layers and TCP/IP 4 Layers
• TCP/IP Packet, TCP vs UDP
• Web Cache
• Cache Validation Headers ETag, If-None-Match
• L1, L2, L3, L4, L5, L6, L7 Switches
• WebSocket, Difference from HTTP
• SSL (Security Socket Layer), TLS (Transfer Layer Security)
• Message Queue (MQ) Concepts
• Subnetting & Supernetting Concepts and Easy Calculation Methods
• 3-way / 4-way Handshake
• Understanding VLANs - VLAN, Trunk, Access Port
• Cache Validation Headers, Last-Modified, If-Modified-Since
• VLAN
• SSL Handshake
• Router
• DHCP(Dynamic Host Configuration Protocol)
• TCP Header
• TCP Session Maintenance Keepalive
• TCP Flag, ECN
• Three QoS Implementation Models (Best Effort, IntServ, DiffServ)
• Token Ring, Ethernet
• Network Lines, VPN, DWDM
• Network Components
• Mac Address, IP Address
• Gateway, Subnet
• Switch in Action
• TCP State Machine
• HTTP Keep-Alive, TCP Keep-Alive
• HTTP Keep-Alive
• File Descriptor in Network(cc. KeepAlive)
• BGP(Border Gateway Protocol) Peering
• IPsec
• SYN Cookie
• TCP Window Size, MSS, SACK Permitted
• TCP Congestion Control
• Evolution and Standards of Loss-based Algorithms (Reno & CUBIC)
• Modern Networks and Next-Generation Congestion Control (BBR & QUIC)

Operating System #

• Application Software (Computer System General Study Notes)
• Process and Thread
• CPU Scheduling
• Runtime and Compile Time
• Swapping in OS
• HTTP Methods
• Virtual Memory System
• [OS] Operating System Structure and Principles
• Mutex and Semaphore
• Threads and Concurrency
• Definition of Daemon Process
• Application SW_2 (Computer System General Study Notes)
• Computing System
• Page Replacement Algorithms: FIFO, LRU, LFU, MFU, NUR
• Memory Fragmentation
• Hypervisor
• Spinlock, Mutex, Semaphore + Mutex vs. Binary Semaphore
• Compiler Optimization
• IPC(Inter Process Comunication)
• Process Memory Structure
• Cache Memory Structure and Operation
• Memory - Address, Contiguous allocation, MMU
• Paging, Fragmentation, TLB
• UDS, 0000.sock
• Parity bit, Pararell Paritiy, Hamming Code
• Process Architecture
• MMU, TLB, Page Table
• NUMA
• NUMA (Kernel Level)
• Page Cache, Buffer Cache
• Inode (Index Node)
• CPU Out-of-Order Execution, Barrier, Happens-Before
• Copy-on-Write (CoW) and fork() Memory Optimization
• CAS and the ABA Problem
• Lock-Free Data Structures and STM

Data Structure #

• 선형 구조
• LinearList
• Linked List
• Stack
• Queue
• 비선형 구조
• Tree
  • Binary Search Tree (BST)
• Abstract Syntax Tree
• Parse Tree
• AVL Tree
• Red-Black Tree: Red-Black Tree
• B-Tree
  • B-Tree Data Deletion
• Graph
  • Depth-First Search (DFS)
• Breadth-First Search (BFS)
• Data Structures and Algorithms
• Breadth-First Search (BFS)
• Depth-First Search (DFS)
• Greedy Algorithm
• Prim's Algorithm
• Dijkstra's Algorithm
• Bellman-Ford Algorithm
• Floyd-Warshall Algorithm

AI #

• One-Hot Encoding, Multicollinearity
• Overfitting, Underfitting
• Weight, Bias cc. Linear Regression
• Hyperparameters
• Regression Model Performance Metrics
• Logistic Regression Theory
• Training Set Scale Issues
• sklearn
• Support Vector Machine
• Neural Network Perception
• Tensor
• GPU Architecture
  • CUDA
• Operator Fusion, Quantization
• TensorRT
• LLM Architecture & Inference Mechanics
• LLM Agent Architecture
• RAG Advancement Strategies
• Image Feature Extraction Feature Extraction
• ORB (Oriented FAST and Rotated BRIEF)
• CNN (Convolution Neural Network) Based Feature Extraction
• LSH(Locality-Sensitive Hashing)
• Elasticsearch Indexing & Vector Search
• Object Detection
• Quantitative Evaluation Metrics for Search Systems (IR Metrics & Evaluation)
• Metric Learning & CLIP
• Approximate Search Algorithms, HNSW (ANN & FAISS)
• Elasticsearch 8.x Native Vector Search and Hybrid Architecture
• AI Model Optimization and Inference Acceleration with ONNX & TensorRT
• AI Serving Architecture (Triton Inference Server & Dynamic Batching)
• Triton Inference Server
• vLLM
• LLM/Agent 공통 플랫폼 아키텍처
  • LLM Gateway and Integrated Routing for Multi-Model (SaaS & Self-hosted)
• Modular RAG Pipeline and Integrated Interface Design
• AI Agent Tooling and Dynamic Prompt/Context Management Platform
• RAG and Agent Serving Pipeline
• LLM/Agent Quantitative Evaluation System
• Multi-tenant LLM Platform Environment and Resource Isolation
• Implementing and Optimizing AI Serving Infrastructure for High-Volume Traffic
  • Model Optimization and Inference Latency Optimization Pipeline
• Tuning Triton Inference Server config.pbtxt
• vLLM Engine Memory Optimization Based on PagedAttention
• Implementing a High-Performance Asynchronous API Layer Communicating with a Core Inference Engine
• Continuous Batching Algorithm
• Nesight Systems, PyTorch Profiler VRAM Memory Bottleneck Profiling
• Implementing LLM Gateway and Multi-Tenant Environment Architecture
  • LiteLLM Proxy Server Configuration
• Tenant-Specific Request Isolation and Authorization Middleware Development
• Token Bucket-Based Rate Limiting
• Implementing Noisy Neighbor Blocking Logic
• Observability Pipeline for Latency-Free Prompt Token Usage Logging
• Processing LLM API Responses
• Implementing State Machine-Based Agent Pipeline Core Logic
  • Agent DAG based on LangGraph
• Evolution from RNN to Attention
  • Checkpointing Application
• Self-Attention, Multi-Head Attention
  • Agent Context Identification Router in Stateless Protocols
• Positional Encoding, Encoder-Decoder
• BERT, GPT
• SFT and Policy Learning
• Off-policy Distillation and Teacher-Student Learning
• On-policy SFT and Rejection Sampling Fine-Tuning
• Preference Optimization: DPO Family
• Online RL: PPO, GRPO, RLVR
• Self-Distillation and Iterative Self-Improvement
• Policy Distribution and On-policy / Off-policy Theory
• LLM Model Tuning Engineer Study
  • Understanding Transformer and Causal LM Architectures
• Tokenizer and Context Length
• Understanding Pretraining Objectives and Loss
• Base Model, Instruct Model, Chat Model
• Differences Between Continual Pretraining and Fine-tuning
• Distinguishing Pretraining Data and SFT Data
• Hermes Agent, Agent Memory Layer
• Archaeology of OpenWeight Models (Kimi, GLM, Qwen, DeepSeek)
  • DeepSeek
• Qwen
• GLM
• Kimi
• Mastering the LLM Inference Serving Engine SGLang
• Long-Term Memory Research
• QWEN Model Analysis
• Kimi Model Analysis
• GLM-5.3 Analysis
• DeepSeek V4.1 Flash Archaeology
• SIFT, SURF
• Adaptive Retrieval for Agents

AI/MLOps #

• CPU and GPU Design Philosophy Differences: Latency Optimization (CPU) vs Throughput Optimization (GPU)
• GPU Thread Execution Model
• GPU Internal Memory Hierarchy
• CUDA, Tensor Core
• HBM, Roofline Model
• PCIe Lane Structure, GPUDirect Storage, NUMA Optimization
• NVLink, NVSwitch
• ZeRO Optimizer (DeepSpeed, FSDP)
• Understanding Transformer Inference Execution Structure
• LLM Serving Benchmarks and Performance Metrics
• KV Cache and Batching Optimization
• 4. Quantization and Multi-GPU Parallelism
• Production Model Serving and Capacity Planning
• Agent Components and State Model Design
• Tool Calling and MCP-based Tool Design
• Durable Execution and Workflow Recovery
• GPU Hardware and Performance Models
• SGLang Serving Casebook
• Serving Playbook by Model Architecture
• Parallelization Strategies — TP, PP, EP, DP
• How a Model Loads onto a GPU
• Distributed Serving and Communication

Mathematics #

• Mathematics
  • Systems of Linear Equations and Matrices
• Gauss-Jordan Elimination and Various Matrices
• Vector Spaces and Inner Products
• Linear Transformations and the Rank-Nullity Theorem
• Eigenvalues and the Cayley-Hamilton Theorem
• Matrix Decomposition
• 선형대수 실습 노트북 (LU·QR·고윳값·SVD)