SidekiqScheduler

Description

sidekiq-scheduler is an extension to Sidekiq that adds support for queueing jobs in the future.

At the moment job scheduling is only supported in a delayed fashion. Replacing cron is not the intention of this gem. Delayed jobs are Sidekiq jobs that you want to run at some point in the future.

The syntax is pretty explanatory:

MyWorker.perform_in(5.days, 'arg1', 'arg2') # run a job in 5 days
# or
MyWorker.perform_at(5.days.from_now, 'arg1', 'arg2') # run job at a specific time

Installation

# Rails 3.x: add it to your Gemfile
gem 'sidekiq-scheduler'

# Starting the scheduler
bundle exec sidekiq-scheduler

The scheduler will perform identically to a normal sidekiq worker with an additional scheduler thread being run - in the default configuration this will result in 25 worker threads being available on the scheduler node but all normal configuration options apply.

NOTE: Since it's currently not possible to hook into the default option parsing provided by sidekiq you will need to use a configuration file to override the scheduler options. Currently the only option available is

resolution: <seconds between schedule runs>

The scheduling thread will sleep this many seconds between looking for jobs that need moving to the worker queue. The default is 5 seconds which should be fast enough for almost all uses.

NOTE: You DO NOT want to run more than one instance of the scheduler. Doing so will result in the same job being queued multiple times. You only need one instance of the scheduler running per application, regardless of number of servers.

NOTE: If the scheduler thread goes down for whatever reason, the delayed items that should have fired during the outage will fire once the scheduler is started back up again (even if it is on a new machine).

Delayed jobs

Delayed jobs are one-off jobs that you want to be put into a queue at some point in the future. The classic example is sending email:

MyWorker.perform_in(5.days, current_user.id)

This will store the job for 5 days in the Sidekiq delayed queue at which time the scheduler will pull it from the delayed queue and put it in the appropriate work queue for the given job. It will then be processed as soon as a worker is available (just like any other Sidekiq job).

NOTE: The job does not fire exactly at the time supplied. Rather, once that time is in the past, the job moves from the delayed queue to the actual work queue and will be completed as workers are free to process it.

Also supported is MyWork.perform_at which takes a timestamp to queue the job.

The delayed queue is stored in redis and is persisted in the same way the standard Sidekiq jobs are persisted (redis writing to disk). Delayed jobs differ from scheduled jobs in that if your scheduler process is down or workers are down when a particular job is supposed to be processed, they will simply "catch up" once they are started again. Jobs are guaranteed to run (provided they make it into the delayed queue) after their given queue_at time has passed.

One other thing to note is that insertion into the delayed queue is O(log(n)) since the jobs are stored in a redis sorted set (zset). I can't imagine this being an issue for someone since redis is stupidly fast even at log(n), but full disclosure is always best.

Removing Delayed jobs

If you have the need to cancel a delayed job, you can do it like this:

# after you've enqueued a job like:
MyWorker.perform_at(5.days.from_now, 'arg1', 'arg2')
# remove the job with exactly the same parameters:
MyWorker.remove_delayed(<timestamp>, 'arg1', 'arg2')

Note on Patches / Pull Requests

Fork the project.
Make your feature addition or bug fix.
Add tests for it. This is important so I don't break it in a future version unintentionally.
Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
Send me a pull request. Bonus points for topic branches.

Credits

This work is a partial port of resque-scheduler by Ben VandenBos.
Modified to work with the Sidekiq queueing library by Morton Jonuschat.