Back-End Development Development 4

Question 1

What is the difference between optimistic and pessimistic locking in databases?

Accepted Answer

Optimistic locking assumes conflicts are rare and checks at commit time; pessimistic locking locks records upfront

Answer

Optimistic locking detects conflicts at commit time using version numbers, while pessimistic locking acquires locks immediately to prevent concurrent modification.

Question 2

Which HTTP/2 feature most improves performance over HTTP/1.1 for back-end APIs serving multiple resources?

Accepted Answer

Multiplexing multiple streams over a single connection

Answer

HTTP/2 multiplexing allows multiple concurrent requests and responses over a single TCP connection, eliminating HTTP/1.1's head-of-line blocking.

Question 3

In a message queue system, what does 'dead letter queue' (DLQ) refer to?

Accepted Answer

A special queue that receives messages that fail processing after maximum retries

Answer

A dead letter queue captures messages that cannot be processed successfully after repeated attempts, enabling debugging without losing the messages.

Question 4

What is N+1 query problem in ORM usage?

Accepted Answer

Running one query to fetch a list, then one additional query per item to fetch related data

Answer

The N+1 problem occurs when fetching a list of N records triggers N additional queries to load their associations, which is solved by eager loading (e.g., JOIN or include).

Question 5

Which algorithm is commonly used for consistent hashing in distributed caching systems?

Accepted Answer

Ring-based consistent hashing

Answer

Consistent hashing places nodes and keys on a virtual ring so that adding or removing nodes only remaps a minimal fraction of keys.

Back-End Development Practice Test

Back-End Development Practice Test

Back-End Development Development 4