OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~149 words · 1 min

Representing a Graph A graph is a set of vertices connected by edges. The two common representations trade memory for lookup speed differently, and the right choice depends on how dense the graph is and what operations dominate. BFS vs DFS

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Software · L2 · Data Structures & Algos: Graph Traversal

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Note~131 words · 1 min

Cache Strategies at a Glance Every caching strategy is really a decision about when the cache and the database are allowed to disagree, and for how long. Which Strategy Fits? The deciding factors are usually how tolerant the application is

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Software · L2 · System Design: Choosing a Cache Strategy

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Note~149 words · 1 min

Why Isolation Levels Exist When multiple transactions run at once, the database has to decide how much of each other's in-progress work they can see. A stricter isolation level prevents more anomalies but forces more transactions to wait on

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Software · L2 · SQL: Isolation Levels & Locking

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Note~92 words · 1 min

When Git Can't Auto-Merge A conflict means two branches changed the same lines and Git needs a human to decide the outcome. It marks the disputed section directly in the file rather than guessing. Staging a file with `git add` after editing

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Software · L2 · Git & Dev Workflow: Resolving a Merge Conflict

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Note~148 words · 1 min

Match the Tool to the Coordination Problem Go's concurrency toolbox isn't one-size-fits-all. Mutexes, channels, and wait groups solve three different problems, and reaching for the wrong one usually means fighting the language instead of wr

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Software · L2 · Go: Choosing a Concurrency Primitive

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Note~142 words · 1 min

Match the Failure Mode to the Type Rust gives you three distinct ways to represent something not going as planned, and each one tells the caller a different story about how serious the situation is. Working Through It Library code in partic

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Software · L2 · Rust: Option, Result, or panic!?

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Note~189 words · 1 min

Threads: Running Code Concurrently A Thread is an independent path of execution within a program. Java can run many threads at once (on multi-core hardware, truly in parallel), letting one program do several things without blocking. You sta

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Software · L2 · Java: Concurrency Basics

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Note~92 words · 1 min

Where the Accessible Name Comes From An interactive element's 'accessible name' — what a screen reader actually reads aloud — is computed by checking several sources in a strict priority order, stopping at the first match. An element marked

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Software · L2 · HTML & CSS: Computing an Element's Accessible Name

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Note~107 words · 1 min

Request In, Response Streamed Out A raw Node HTTP server has no built-in middleware concept, but the pattern is simple: an ordered list of functions, each given the chance to act or hand off control to the next one via `next()`. Because Inc

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Software · L2 · Node.js: HTTP Middleware Pipeline

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Note~105 words · 1 min

Delegated Access Without Sharing Passwords The authorization code flow lets a third-party client obtain limited access to a user's account on another service, by routing the login through that service's own authorization server. Public clie

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Software · L2 · Networking & HTTP: OAuth 2.0 Authorization Code Flow

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Note~129 words · 1 min

What Matters Most? No scheduling algorithm is best on every axis — each one optimizes for a particular goal at the expense of another. Picking one starts with naming what the workload actually needs. A Decision Path In practice, most genera

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Software · L2 · Operating Systems: Choosing a CPU Scheduling Algorithm

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Note~151 words · 1 min

Same Goal, Different Tools All synchronization primitives exist to keep concurrent access to shared state correct, but they differ in how many threads they let through at once, whether they track ownership, and whether they block or spin wh

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Software · L2 · Concurrency: Choosing a Synchronization Primitive

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Note~125 words · 1 min

When Something Goes Wrong Prevention fails sometimes, no matter how strong your defenses. Incident response is the practiced sequence a team follows once an attack or breach is confirmed, so the reaction is fast and consistent rather than i

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Software · L2 · Security & Auth: Incident Response Basics

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Note~119 words · 1 min

From Commit to Production A CI/CD pipeline is a chain of gates: each stage exists to catch a specific class of problem before it reaches the next, more expensive, stage. Test always runs before Package/Publish: it's cheaper to fail the pipe

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Software · L2 · Docker & Kubernetes: CI/CD Pipeline Stages

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Note~119 words · 1 min

Not Every Test Runs at Every Gate A mature CI setup doesn't run the entire suite everywhere — it matches test speed to how often the gate fires, so fast feedback stays fast and thorough coverage still happens somewhere. Notice E2E tests run

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Software · L2 · Testing: CI Test Execution Strategy

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Note~129 words · 1 min

Same Shape, Different Intent Adapter, Decorator, and Proxy all wrap one object behind an interface, which is exactly why they're easy to confuse. The difference is in what the wrapper is for: translating, extending, or controlling. A Decisi

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Software · L2 · Design Patterns: Which Structural Pattern?

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Note~162 words · 1 min

Mapping Entities and Relationships A JPA entity is a POJO annotated `@Entity` with an `@Id` field, mapped to a database table. Relationships between entities are declared with annotations rather than manual join SQL. Why @Transactional Matt

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Software · L2 · Spring Boot: Data Access & Transactions

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Note~163 words · 1 min

Catching by Type with `on` A plain `catch (e)` catches anything thrown. `on SomeType catch (e)` catches only that type, letting you stack multiple `on` clauses to handle different error types differently, with a general `catch` as a fallbac

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Software · L2 · Dart: Error Handling & Testing

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Note~151 words · 1 min

Fetching JSON with the http Package `http.get(Uri.parse(url))` returns a Future<Response> with a status code and body string. Check `response.statusCode == 200` before decoding, then use `jsonDecode(response.body)` (from dart:convert) to tu

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Software · L2 · Flutter: Networking & Data

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Note~165 words · 1 min

One File, Every Matching Request A `middleware.ts` at the project root runs before a request reaches its matched route — redirecting, rewriting, setting headers/cookies, or gating access based on auth, all before any page or route handler c

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Software · L2 · Next.js: Middleware & Edge Runtime

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Note~109 words · 1 min

Four Ways to Satisfy a Token A provider isn't always 'a class Nest instantiates for you' — the `providers` array can register several different shapes, each resolved differently when a token is requested. Whichever shape produces the instan

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Software · L2 · NestJS: Custom Provider Resolution

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Note~110 words · 1 min

What Is a Replica Set? A replica set is a group of mongod processes holding the same data set. One member is the primary and accepts all writes; the rest are secondaries that replicate the primary's operations from its oplog (operation log)

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Software · L2 · MongoDB: Replica Sets & Failover

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Note~134 words · 1 min

Streaming Replication Every write to a Postgres primary is first recorded in the Write-Ahead Log (WAL). Streaming replication ships that WAL to one or more standby servers, which replay it to reconstruct an up-to-date copy of the data — wit

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Software · L2 · PostgreSQL: Replication & High Availability

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Note~107 words · 1 min

The Pipeline Stages AWS splits CI/CD into three composable services rather than one monolithic tool. CodePipeline orchestrates the stages, CodeBuild compiles and tests, and CodeDeploy rolls the result out to running infrastructure. What Hap

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Software · L2 · AWS: CI/CD Pipelines

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Note~111 words · 1 min

The Build-to-Release Chain GCP separates CI/CD into focused services: Cloud Build compiles and tests, Artifact Registry stores the resulting images/packages, and Cloud Deploy manages progressive rollout to your runtime of choice. What Happe

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Software · L2 · Google Cloud: CI/CD & Deployment

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Note~138 words · 1 min

Why Two Concurrent Applies Are Dangerous State is Terraform's single source of truth for what it manages. If two applies write to it at once, the file can end up corrupted or missing resources — a remote backend with locking exists specific

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Software · L2 · Terraform: Safe Applies with Remote State & Locking

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Note~581 words · 3 min

Resources, Not Actions A REST API is organized around resources — nouns like orders, users, or invoices — addressed by URLs, with the HTTP method supplying the verb. A well-modeled API reads as a set of collections and items: /orders is a c

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Software · L3 · API Design & REST

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Note~575 words · 3 min

Why Cache at All A cache trades memory for latency: keeping a copy of expensive-to-compute or expensive-to-fetch data somewhere faster to read than the source of truth. The two design questions that matter most are how reads and writes flow

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Software · L3 · Caching Strategies

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Note~557 words · 3 min

Pure Functions and Side Effects A pure function's return value depends only on its arguments, and calling it has no observable effect beyond producing that value — no writing to a database, mutating a shared object, logging, or reading the

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Software · L3 · Functional Programming Concepts

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Note~560 words · 3 min

How a Backtracking Engine Matches Most mainstream regex engines (PCRE, Python's re, JavaScript's RegExp) are backtracking engines: they try the pattern against the input greedily, and whenever a later part fails to match, they backtrack to

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Software · L3 · Regular Expressions & Text Parsing

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