Common Performance Questions

A "good" response time is highly context-dependent. For interactive web applications, users typically expect response times under 2-3 seconds. For API calls or background processes, acceptable times can be much longer. Key metrics include Time to First Byte (TTFB), First Contentful Paint (FCP), and Largest Contentful Paint (LCP).

Performance can be measured using various tools and techniques:

• Browser Developer Tools: Chrome DevTools (Lighthouse, Network, Performance tabs), Firefox Developer Tools.
• Synthetic Monitoring: Tools like GTmetrix, Pingdom, WebPageTest simulate user visits from different locations.
• Real User Monitoring (RUM): Tools that collect performance data from actual users in real-time (e.g., Google Analytics, Datadog RUM).
• Server-side Monitoring: Application Performance Monitoring (APM) tools like New Relic, Dynatrace, AppDynamics monitor backend processes.
• Load Testing: Tools like JMeter, k6, Artillery simulate high user traffic to identify bottlenecks.

Common bottlenecks include:

• Network Latency: Slow connection speeds, high ping times.
• Server Overload: Insufficient CPU, memory, or I/O capacity.
• Inefficient Database Queries: Unoptimized queries, missing indexes, N+1 query problems.
• Large Assets: Unoptimized images, large JavaScript/CSS files.
• Render-Blocking Resources: JavaScript or CSS that prevents the page from rendering quickly.
• Third-Party Scripts: Slow-loading external scripts can block the main thread.
• Client-Side Processing: Heavy JavaScript computations on the user's browser.

Optimizing images is crucial:

• Choose the Right Format: Use WebP for modern browsers, JPEG for photos, PNG for graphics with transparency, SVG for vector art.
• Compress Images: Use tools like TinyPNG, ImageOptim, or online compressors to reduce file size without significant quality loss.
• Responsive Images: Use the <picture> element or srcset attribute to serve appropriately sized images based on the user's device.
• Lazy Loading: Defer loading of images that are below the fold using the loading="lazy" attribute.
• Serve Images from a CDN: Content Delivery Networks reduce latency by serving images from servers geographically closer to the user.

Caching is the process of storing copies of files or data in a temporary storage location (cache) so that they can be accessed more quickly. This reduces the need to fetch data from the original, slower source.

Types of caching include:

• Browser Caching: Stores static assets (CSS, JS, images) on the user's browser.
• Server-Side Caching: Caches database query results, rendered HTML pages, or API responses on the server.
• CDN Caching: Caches static assets at edge locations worldwide.
• In-Memory Caching: Uses fast in-memory data stores like Redis or Memcached for frequently accessed data.

By serving cached content, applications reduce server load and decrease response times, leading to a faster user experience.

HTTP/2 offers significant performance improvements over HTTP/1.1:

• Multiplexing: Allows multiple requests and responses to be sent over a single TCP connection concurrently, eliminating head-of-line blocking.
• Header Compression (HPACK): Reduces the overhead of HTTP headers, especially important for many small requests.
• Server Push: Allows the server to send resources to the client that it anticipates the client will need, before the client explicitly requests them.
• Binary Framing: More efficient than HTTP/1.1's text-based protocol.

These features collectively reduce latency and improve the speed at which web pages load.