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All fields Software Mathematics Physics Chemistry Biology Engineering Astronomy Environmental Other Software Software groups

Explore STEM Content

Search the community's STEM library — free to study, yours to make your own.

Software

Programming, algorithms and systems on openstem — flashcards, notes, quizzes, sketches and flowcharts shared by the community. Study free, or clone anything into your library.

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Flashcards10 cards

How does a WebSocket connection start?1 / 10

It begins as an HTTP request with an Upgrade: websocket header; if the server accepts (101 Switching Protocols), the connection switches to a persistent full-duplex WebSocket.

Software

WebSockets & Real-time

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WebSockets & Real-time

Flashcards10 cards

What does `FutureBuilder` do?1 / 10

It rebuilds its widget subtree based on the latest snapshot of a Future, exposing connection state, data, and error so you can render loading, success, and failure UIs.

Software

Async & Networking

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Async & Networking

Flashcards10 cards

How does a `for` loop differ in Go from C-style languages?1 / 10

Go has a single `for` keyword that serves as for, while, and infinite loops. `for {}` is infinite, `for cond {}` is a while loop, and `for i := 0; i < n; i++ {}` is the classic three-clause form.

Software

Syntax & Control Flow

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Syntax & Control Flow

Quiz5 questions

What does `COMMIT` do at the end of a transaction?

AUndoes every statement since BEGINBMakes every statement since BEGIN permanentCLocks the table permanentlyDDeletes the transaction log

Software

Software · L1 · SQL: Transactions & ACID

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Software · L1 · SQL: Transactions & ACID

Flashcards7 cards

Define a dataflow analysis in terms of transfer functions and a lattice.1 / 7

A dataflow analysis assigns each program point a value from a lattice (L, ⊑) representing an abstract fact (e.g. the set of live variables). Each CFG edge/statement has a transfer function f: L → L propagating facts across it; the analysis computes, for every point, the least fixpoint of these equations subject to a meet (∩) or join (∪) at control-flow merge points, depending on whether the analysis is 'must' or 'may'.

Software

Software · L5 · Program Analysis & Abstract Interpretation

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Software · L5 · Program Analysis & Abstract Interpretation

Flowchart15 objects

Software

Software · L2 · Design Patterns: Which Structural Pattern? · flowchart

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Software · L2 · Design Patterns: Which Structural Pattern? · flowchart

Flashcards10 cards

How do you approach a back-of-envelope capacity estimation?1 / 10

Estimate: DAU × actions per user = requests/day → requests/second (÷86400). Estimate storage: requests × payload size. Estimate bandwidth: RPS × payload. Benchmark memory, CPU, and network against known reference points (1 Gbps NIC, 100MB/s disk, 1M ops/s Redis). Simplify with round numbers.

Software

System Design Practice

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System Design Practice

Flowchart15 objects

Software

Software · L1 · Docker & Kubernetes: Image Build & Deploy Lifecycle · flowchart

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Software · L1 · Docker & Kubernetes: Image Build & Deploy Lifecycle · flowchart

Collection5 items

01Generics & Utility Types

02Patterns & Best Practices

03Modules & Declaration Files

+2 more

Software

Software · L2 · TypeScript

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Software · L2 · TypeScript

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

Software

Software · L2 · PostgreSQL: Replication & High Availability

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Software · L2 · PostgreSQL: Replication & High Availability

Flashcards10 cards

What does ACID stand for in database transactions?1 / 10

Atomicity (all or nothing), Consistency (valid state transitions only), Isolation (concurrent transactions don't interfere), Durability (committed data survives crashes). Most relational DBs guarantee ACID by default.

Software

Transactions & ACID

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Transactions & ACID

Note~710 words · 4 min

Applied Cryptography for Engineers Most engineers never implement a cipher, but every engineer builds systems that depend on cryptographic primitives being composed correctly. The failures that matter in practice are almost never 'AES was b

Software

Software · L4 · Applied Cryptography for Engineers

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Software · L4 · Applied Cryptography for Engineers

Note~135 words · 1 min

Match the Data Shape to the Database There is no single 'best' database — each type trades away something (joins, flexibility, raw speed) to excel at a particular access pattern. Picking well starts with describing the shape of the data and

Software

Software · L1 · System Design: Choosing a Database Type

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Software · L1 · System Design: Choosing a Database Type

Collection4 items

01Rust Syntax & Basics

02Ownership & Borrowing

03Software · L1 · Rust: Move, Borrow, or Clone?

+1 more

Software

Software · L1 · Rust

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Software · L1 · Rust

Flashcards9 cards

What is a metaclass in Python and what is it used for?1 / 9

A metaclass is a class whose instances are classes. `type` is the default metaclass. Custom metaclasses (by subclassing `type`) can intercept class creation to auto-register subclasses, validate class structure, or add methods automatically. Define with `class Meta(type): ...` and use `class MyClass(metaclass=Meta)`.

Software

Advanced Python

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Advanced Python

Collection7 items

01Software · L2 · Loops: Doing Things Again and Again

02Software · L2 · Variables: Labelled Boxes for Values

03Software · L2 · How the Internet Works

+4 more

Software

Software · L2 · Patterns & Practice

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Software · L2 · Patterns & Practice

Collection4 items

01Core Java

02Syntax & Control Flow

03Software · L1 · Java: Classes & Objects

+1 more

Software

Software · L1 · Java

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Software · L1 · Java

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

Software

Software · L2 · NestJS: Custom Provider Resolution

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Software · L2 · NestJS: Custom Provider Resolution

Flashcards10 cards

What is the main trade-off introduced by applying many design patterns?1 / 10

Patterns add indirection and abstraction. Used well they decouple and clarify; used excessively they obscure control flow and raise cognitive load. The trade-off is flexibility vs simplicity.

Software

Applying Patterns at Scale

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Applying Patterns at Scale

Quiz6 questions

Which statement correctly distinguishes data parallelism from model parallelism?

AData parallelism partitions the model across devices; model parallelism replicates itBData parallelism replicates the full model and shards the data across workers; model parallelism partitions the model itself because it does not fit on one deviceCThe two terms are synonyms for the same techniqueDData parallelism requires a parameter server; model parallelism never does

Software

Software · L5 · Distributed Machine Learning Systems

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Software · L5 · Distributed Machine Learning Systems

Flashcards10 cards

What problem does Docker Compose solve?1 / 10

Compose defines and runs multi-container applications from a single YAML file. Instead of many `docker run` commands, you declare services, networks, and volumes once and start them all with `docker compose up`.

Software

Docker Compose Fundamentals

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Docker Compose Fundamentals

Collection4 items

01Terraform Fundamentals

02IaC Fundamentals

03Software · L1 · Terraform: The Core Workflow

+1 more

Software

Software · L1 · Terraform

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Software · L1 · Terraform

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

Software

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

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

Flashcards10 cards

What lives on the heap versus the stack in the JVM?1 / 10

Objects and their instance fields live on the shared heap (garbage-collected), while each thread's stack holds frames with local variables and references to heap objects.

Software

JVM & Memory Model

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JVM & Memory Model

Flowchart12 objects

Software

Software · L2 · SQL: Isolation Levels & Locking · flowchart

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Software · L2 · SQL: Isolation Levels & Locking · flowchart

Flashcards10 cards

What does calling `setState` do in a StatefulWidget?1 / 10

It notifies the framework that internal state has changed, scheduling a rebuild of the widget's `build` method. Mutations should happen inside the setState callback.

Software

State Management

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State Management

Flashcards9 cards

What does `go vet` do?1 / 9

`go vet` is a static analysis tool that reports suspicious constructs the compiler accepts but are likely bugs, such as mismatched Printf format verbs or unreachable code.

Software

Standard Library & Tooling

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Standard Library & Tooling

Flowchart11 objects

Software

Software · L1 · Data Structures & Algos: Picking the Right Approach · flowchart

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Software · L1 · Data Structures & Algos: Picking the Right Approach · flowchart

Flashcards10 cards

What does the `await` keyword do inside an `async` function?1 / 10

It suspends the function until the awaited Future completes, then resumes with its result. The surrounding function returns a Future immediately to its caller.

Software

Async & Futures

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Async & Futures

Collection4 items

01Fundamentals

02Syntax & Control Flow

03Software · L1 · Go: new(), make(), or a Literal?

+1 more

Software

Software · L1 · Go

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Software · L1 · Go

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