Back-End Development Back-End Performance and Caching 2

Question 1

What is a cache eviction policy and what does LRU stand for?

Accepted Answer

The strategy for removing cached items when the cache is full — Least Recently Used means removing the item accessed least recently

Answer

Cache eviction policies determine which items to remove when the cache reaches capacity; LRU (Least Recently Used) evicts the item that hasn't been accessed for the longest time.

Question 2

What is the thundering herd problem in caching?

Accepted Answer

A situation where many requests simultaneously hit the origin/database when a popular cached item expires

Answer

The thundering herd occurs when a highly-requested cached item expires simultaneously for all callers, causing a surge of requests to hit the database at once before the cache is repopulated.

Question 3

What is HTTP caching and which header controls cache duration for browser and CDN caching?

Accepted Answer

Browser and CDN caching of HTTP responses — controlled by the Cache-Control header

Answer

The Cache-Control header (e.g., max-age=3600, public) instructs browsers and CDNs how long to cache a response, reducing server load and improving client-perceived performance.

Question 4

What is the purpose of database query optimization techniques like selecting only needed columns?

Accepted Answer

To minimize the amount of data transferred from the database, reducing memory use and network overhead

Answer

Using SELECT column1, column2 instead of SELECT * limits data retrieval to only needed fields, reducing memory consumption, network bandwidth, and the chance of exposing sensitive columns.

Question 5

What is async/await and why is it important for back-end I/O performance in Node.js?

Accepted Answer

Syntax sugar over Promises that allows non-blocking I/O operations, keeping the event loop free to handle other requests while waiting

Answer

async/await enables writing asynchronous code that reads like synchronous code while keeping Node.js's single-threaded event loop free during I/O waits, allowing the server to handle thousands of concurrent requests efficiently.

Back-End Development Practice Test

Back-End Development Practice Test

Back-End Development Back-End Performance and Caching 2