Question: What are some common use cases of BullMQ?

Answer

BullMQ is a fast, reliable and highly customizable priority job queue for Node.js, based on the Redis database. Here are some common use cases of BullMQ:

1. Background Jobs: One of the most common use cases of BullMQ is running tasks or jobs in the background that don't need to be executed instantly. This can range from sending emails, processing images, to data analytics and more.

const Queue = require('bull');
const myQueue = new Queue('myQueue');

myQueue.add({
  email: 'example@example.com',
  subject: 'Welcome',
  message: 'Thank you for joining us!'
});

2. Delayed Jobs: You can schedule jobs that run after a certain delay. This could be useful for reminders, notifications, or any task that should only be performed after some time.

myQueue.add({
  email: 'example@example.com',
  subject: 'Subscription ending soon',
  message: 'Your subscription will end in 3 days.'
}, {
  delay: 3 * 24 * 60 * 60 * 1000 // 3 days in milliseconds
});

3. Priority Jobs: If there are jobs that need to be executed before others, BullMQ provides a priority system. Higher priority jobs get processed first.

// High priority job
myQueue.add({
  email: 'example@example.com',
  subject: 'High Priority',
  message: 'This is a high priority job'
}, { priority: 1 }); 

// Low priority job
myQueue.add({
  email: 'example@example.com',
  subject: 'Low Priority',
  message: 'This is a low priority job'
}, { priority: 2 }); 

4. Rate Limited Jobs: For tasks that should not be performed too frequently, you can set a rate limit on your job queue.

const rateLimitedQueue = new Queue('emailNotifications', {
  limiter: {
    max: 100,
    duration: 60000 // 100 jobs per minute
  }
});

5. Repeated Jobs: BullMQ can schedule jobs to be run repeatedly at fixed intervals, similar to a cron job.

myQueue.add({
  data: 'Repeat this job every day'
}, { repeat: { cron: '* * * * *' } }); // Cron syntax for every minute

Remember that usage patterns can vary widely depending on the specific needs of your application. These are just some of the highlights of what BullMQ has to offer.