The main goal is to delay some nonessential tasks to later, reducing the waiting time for the user.
Let's say a lambda user wants to update his location, and your website has some pretty neat social features centered around the user.
Main workflow for the update location action :
- Update the user's location in the users table (or whatever, depending on your structure)
-> took 0.2s
- Refresh various cache
-> took 0.1s
- Send mails
-> took 0.7s
- Send some notifications to all your friends
-> took 3.7s
- Recommend some new friends around your new location
-> took 2s
Total time : 3.7 seconds
Your mileage may vary, but what to remember here is that the important stuff takes just a fraction of the total processing time.
But the user doesn't sadly care about all of these stuffs, and just want to update his location.
Why should the user wait for the cache refresh ? It does not matter at all if it refreshed or not in the final response return to the user.
And what will happen if there's an error while refreshing the cache ?
- Answer A : It crashes the application (you should review your code …)
- Answer B : Ignore it, and continue (who will do it then ?)
The problem here is that there're some actions in the main workflow that :
- are not required to be executed immediately
- are prone to errors, and could take down your entire application
- can take time to process, thus slowing the total processing time
- can cost system resources
User should just wait 0.2s instead of 3.7s
A response should be returned immediately after the first point, and delay all the other tasks for later, out of the main workflow. That way, "unimportant" tasks doesn't affect the main workflow.
The trick is to tell someone else to do it.
Here come the background jobs.
Instead of executing the task, we convert it into a job, then put it in a queue. A worker, which is running on another php process, will poll that queue and execute the job.
That queue system is based on Resque. CakeResque is just wrapper of Resque for CakePHP.
Resque (pronounced like "rescue") is a Redis-backed library for creating background jobs, placing those jobs on multiple queues, and processing them later.
- Resque official page
- Php-Resque : PHP port of Resque
- Serie of 9 tutorials explaining the mechanic behind backgound jobs
All support, bugs submissions and feature requests are tracked on Github.
Wan Qi Chen
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