#Performance

122 questions

What are streams in Node.js and when should you use them?Node.js#streamsMiddle
How do you scale a Node.js app across multiple CPUs?Node.js#scalingSenior
How do you detect and fix memory leaks in Node.js?Node.js#debuggingSenior
When and how do you use worker threads?Node.js#performanceMiddle
What caching strategies improve a Node API's performance?Node.js#performanceMiddle
How do you profile and optimize Node.js performance?Node.js#performanceSenior
What is backpressure in streams and how do you handle it?Node.js#streamsSenior
What is the difference between blocking and non-blocking operations in Node.js?Node.js#asyncMiddle
What kinds of operations block the Node.js event loop?Node.js#asyncMiddle
When should you use useMemo and useCallback, and what problem do they solve?React#hooksSenior
What does React.memo do and when is it worth using?React#performanceMiddle
What are concurrent features like useTransition and useDeferredValue?React#performanceSenior
How do Suspense and React.lazy work for code splitting?React#performanceSenior
How do you diagnose and fix unnecessary re-renders?React#performanceSenior
What is an index in SQL? When should and shouldn't you use one?SQL#indexMiddle
How do you optimize slow SQL queries?SQL#performanceSenior
What is table partitioning?SQL#performanceSenior
How do srcset, sizes and picture serve responsive images?HTML#mediaMiddle
How does the browser parse HTML and build the page (critical rendering path)?HTML#performanceSenior
What is the difference between defer and async on scripts?HTML#performanceSenior
What are resource hints like preload, prefetch and preconnect?HTML#performanceSenior
How does native lazy loading of images/iframes work?HTML#performanceSenior
How do you keep CSS rendering performant (reflow vs repaint)?CSS#performanceSenior
What is the difference between debounce and throttle?JavaScript#performanceSenior
What is memoization and how do you implement it?JavaScript#performanceSenior
How does JavaScript manage memory and how do leaks happen?JavaScript#performanceSenior
What does the next/image component do?Next.js#performanceJunior
What caching layers does Next.js have?Next.js#performanceMiddle
How does streaming SSR with Suspense work in Next.js?Next.js#renderingSenior
How do you optimize performance and Core Web Vitals in Next.js?Next.js#performanceSenior
How does next/font optimize fonts?Next.js#performanceMiddle
What is Partial Prerendering (PPR)?Next.js#renderingSenior
How do async components enable lazy loading?Vue.js#performanceMiddle
How do you optimize performance in a Vue app?Vue.js#performanceSenior
How do you lazy-load routes/features in Angular?Angular#performanceMiddle
How does Angular change detection work, and what does OnPush do?Angular#performanceSenior
What does Angular SSR (Universal) provide?Angular#renderingSenior
What is Zone.js and what does "zoneless" Angular mean?Angular#performanceSenior
How do you keep state updates from causing excessive re-renders?State Management#performanceSenior
How do you add caching in NestJS?NestJS#performanceSenior
How do you optimize NestJS performance?NestJS#performanceSenior
What is the GIL and how does it affect concurrency?Python#concurrencySenior
How does Python manage memory and garbage collection?Python#performanceSenior
When do you choose threading, multiprocessing, or asyncio?Python#concurrencySenior
How do you profile and optimize Python performance?Python#performanceSenior
Why is FastAPI fast, and how do you keep it that way?FastAPI#performanceSenior
How do select_related and prefetch_related avoid the N+1 problem?Django#performanceMiddle
What caching options does Django provide?Django#performanceSenior
How does async support work in modern Django?Django#performanceSenior
How do you scale Django at the database level?Django#performanceSenior
How does Go manage memory and garbage collection?Golang#performanceSenior
How do you profile and optimize Go performance?Golang#performanceSenior
How does JVM memory and garbage collection work?Java#performanceSenior
How do you optimize JVM application performance?Java#performanceSenior
How do you optimize PHP performance (OPcache, JIT)?PHP#performanceSenior
What are generators in PHP and why use them?PHP#performanceSenior
What caching does Laravel provide?Laravel#performanceSenior
How do you fix N+1 queries and optimize Eloquent?Laravel#performanceSenior
How do you deploy and optimize Laravel for production?Laravel#performanceSenior
How does memory management and garbage collection work in .NET?C##performanceSenior
How do Span<T> and Memory<T> improve performance?C##performanceSenior
How does C# code execute (IL, JIT, AOT)?C##performanceSenior
What is boxing and unboxing, and why does it matter?C##performanceMiddle
How does Ruby manage memory and garbage collection?Ruby#performanceSenior
How do you profile and optimize Ruby performance?Ruby#performanceSenior
What does freezing objects do and why use frozen string literals?Ruby#performanceSenior
How do you query 10B records under 100ms?System Design#databaseSenior
How do you import 100M CSV records into a DB fast?System Design#performanceSenior
How do you export a huge dataset without impacting the live system?System Design#performanceMiddle
How do you handle a hot key or hot row under heavy contention?System Design#performanceMiddle
What index types does PostgreSQL offer?PostgreSQL#performanceMiddle
How do you use EXPLAIN and EXPLAIN ANALYZE?PostgreSQL#performanceMiddle
How do materialized views work in PostgreSQL?PostgreSQL#performanceMiddle
How does table partitioning work in PostgreSQL?PostgreSQL#performanceMiddle
How do you bulk-load data efficiently with COPY?PostgreSQL#performanceMiddle
What is VACUUM and why is it important?PostgreSQL#performanceSenior
Why do you need connection pooling (PgBouncer)?PostgreSQL#performanceSenior
How do you tune PostgreSQL performance?PostgreSQL#performanceSenior
How do indexes work in MongoDB?MongoDB#performanceMiddle
How do you optimize MongoDB performance?MongoDB#performanceSenior
What advanced indexing strategies does MongoDB support?MongoDB#performanceSenior
How is Redis used as a cache?Redis#performanceJunior
What caching strategies and patterns exist with Redis?Redis#performanceMiddle
How does Redis manage memory?Redis#performanceMiddle
How do you optimize Redis performance?Redis#performanceSenior
What are the challenges of cache invalidation?Redis#performanceSenior
What is pipelining in Redis and when should you use it?Redis#performanceMiddle
Why is connection pooling important when using Redis?Redis#performanceMiddle
How does caching work on AWS (ElastiCache)?Cloud & AWS#performanceMiddle
A web page or API is slow — how do you find the cause?Site Reliability & Operations#performanceMiddle
How do you optimize a slow database query?Site Reliability & Operations#databaseMiddle
How do you tell whether a bottleneck is CPU, memory, I/O, or network?Site Reliability & Operations#performanceMiddle
How would you tune a high-traffic WordPress site for performance?Site Reliability & Operations#wordpressSenior
What are the cache layers in a typical web stack?Site Reliability & Operations#cachingMiddle
How do you decide what to cache and for how long (TTL)?Site Reliability & Operations#cachingMiddle
What is a cache stampede and how do you prevent it?Site Reliability & Operations#cachingMiddle
An API's p99 latency is 3s — how do you debug and optimize it?Site Reliability & Operations#performanceSenior
How do you optimize SwiftUI performance around view identity and diffing?iOS (Swift & SwiftUI)#swiftuiSenior
What are LCP, CLS, and INP, and what are good thresholds?Web Performance & Core Web Vitals#performanceJunior
What is the critical rendering path and what blocks it?Web Performance & Core Web Vitals#performanceJunior
How do you lazy-load images and components, and why?Web Performance & Core Web Vitals#performanceJunior
What makes a JS bundle grow, and why does size hurt?Web Performance & Core Web Vitals#performanceJunior
How do you diagnose and improve a slow LCP?Web Performance & Core Web Vitals#performanceMiddle
What causes layout shift, and how do you fix CLS?Web Performance & Core Web Vitals#performanceMiddle
What are code splitting and tree shaking?Web Performance & Core Web Vitals#performanceMiddle
How does HTTP caching work with immutable assets and a CDN?Web Performance & Core Web Vitals#performanceMiddle
How do you optimize images: formats, srcset, and priority?Web Performance & Core Web Vitals#performanceMiddle
Lighthouse vs RUM: how do you measure performance properly?Web Performance & Core Web Vitals#observabilitySenior
CSR vs SSR vs SSG vs streaming: the performance trade-offs?Web Performance & Core Web Vitals#performanceSenior
How do you diagnose runtime jank, long tasks, and poor INP?Web Performance & Core Web Vitals#performanceSenior
What is the N+1 problem in GraphQL and how does DataLoader fix it?GraphQL#performanceMiddle
How do you tune performance in a Spring Boot app: pools, caching, N+1?Spring Boot#springSenior
How do B-tree, composite, and covering indexes work, and what is the leftmost-prefix rule?MySQL#databaseMiddle
How do you read EXPLAIN and use it to optimize a slow query?MySQL#performanceMiddle
How do you tune a MySQL server: buffer pool, slow query log, and connections?MySQL#performanceSenior
What limits concurrency at scale? Explain contention, false sharing, and backpressure.Concurrency & Parallelism#concurrencySenior
What is the difference between CPU/memory requests and limits, and how do they affect scheduling, eviction, and QoS?Kubernetes#performanceMiddle
What is the difference between latency, bandwidth, and throughput?Networking#networkingSenior
How does CPU scheduling work, and what are the common algorithms?Operating Systems#performanceMiddle
What does a context switch actually cost, and why does it matter?Operating Systems#operating-systemsSenior
How do you design pagination, filtering, and sorting for a collection endpoint?REST API Design#performanceMiddle
How do rate limiting and HTTP caching work in a REST API?REST API Design#apiSenior