Difference between Action Job/Mailer's `deliver_now` and `deliver_later`

Question

The common pattern for interfacing with ActionJob in Rails is to set up a Job with a perform() method that gets called asynchronously via perform_now or perform_later

In the special case of Mailers, you can directly call deliver_now or deliver_later since ActionJob is well integrated with ActionMailer.

The rails documentation has the following comments -

# If you want to send the email now use #deliver_now
UserMailer.welcome(@user).deliver_now

# If you want to send the email through Active Job use #deliver_later
UserMailer.welcome(@user).deliver_later

The wording makes it seem like deliver_now will not use ActiveJob to send the mail. Is that correct, and if so what's the true difference between deliver_now and deliver_later? Is one not asynchronous?

Similarly, does the same difference apply to perform_now and perform_later ?

Thanks!

Answer 1

As you say in your question, deliver_now does not use ActiveJob.

Basically, deliver_later is asynchronous. When you use this method, the email is not send at the moment, but rather is pushed in a job's queue. If the job is not running, the email will not be sent. deliver_now will send the email at the moment, no matter what is the job's state. Here you can see the documentation for deliver methods.

According to your second question, perform_now will process the job immediately without sending to the queue. perform_later, however, will add the job to the queue, and as soon the job's queue is free, will perform the job. Here you can see the documentation for perform methods.