# ActiveJob & Background Jobs (Ruby on Rails)

> ActiveJob, Sidekiq, DelayedJob, job queues, perform_later, error handling, retry logic, GlobalID

- 20 interview questions
- Mid-Level
- [Interview Questions: Ruby on Rails](https://sharpskill.dev/en/technologies/ruby-on-rails/interview-questions.md)

## 1. What is ActiveJob in Ruby on Rails?

**Answer**

ActiveJob is a built-in Rails framework that provides a unified interface for declaring jobs and running them on various queuing backends like Sidekiq, Resque, or DelayedJob. It allows switching backends without modifying job code, offering a standardized abstraction for asynchronous background processing.

## 2. Which method should be used to execute a job asynchronously in ActiveJob?

**Answer**

The perform_later method enqueues the job for asynchronous execution by the configured queuing backend. The job is placed in a queue and will be processed later by a worker. Unlike perform_now which executes the job immediately and synchronously, perform_later frees the main thread and improves application responsiveness.

## 3. What is the main difference between perform_later and perform_now in ActiveJob?

**Answer**

perform_later enqueues the job in a queue for later asynchronous execution by a worker, while perform_now executes the job immediately and synchronously in the current process. perform_now is useful for testing or when immediate execution is required, but it blocks the calling thread until the job completes.

## 17 more questions available

- How to define the default queue for an ActiveJob job?
- What is GlobalID and what is its role in ActiveJob?

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## Other Ruby on Rails interview topics

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