Delated_job (or DJ) encapsulates the common pattern of asynchronously executing longer tasks in the background.
It is a direct extraction from Shopify where the job table is responsible for a multitude of core tasks. Amongst those tasks are:
- sending massive newsletters
- image resizing
- http downloads
- updating smart collections
- updating solr, our search server, after product changes
- batch imports
- spam checks
The library evolves around a delayed_jobs table which looks as follows:create_table :delayed_jobs, :force => true do |table| table.integer :priority, :default => 0 table.integer :attempts, :default => 0 table.text :handler table.string :last_error table.datetime :run_at table.datetime :locked_at table.datetime :failed_at table.string :locked_by table.timestamps end
Jobs are simple ruby objects with a method called perform. Any object which responds to perform can be stuffed into the jobs table.
Job objects are serialized to yaml so that they can later be resurrected by the job runner.
There is also a second way to get jobs in the queue: send_later.BatchImporter.new(Shop.find(1)).send_later(:import_massive_csv, massive_csv)
This will simply create a Delayed::PerformableMethod job in the jobs table which serializes all the parameters you pass to it. There are some special smarts for active record objects which are stored as their text representation and loaded from the database fresh when the job is actually run later.
To get enqueue jobs from the command line, you can use script/runner to execute the above code. If you have a Rails environment that is slow to load, there is a script which will insert a job directly into the database: Run
script/generate delayed_job to add
script/enqueue_job. This script can then be used to queue up some arbitrary ruby code to be executed.
Running the jobs
You can invoke
rake jobs:work which will start working off jobs. You can cancel the rake task with
You can also run by writing a simple
script/job_runner, and invoking it externally:
#!/usr/bin/env ruby require File.dirname(__FILE__) + '/../config/environment' Delayed::Worker.new.start
You can invoke
rake jobs:clear to delete all jobs in the queue.
- 1.7.0: Added failed_at column which can optionally be set after a certain amount of failed job attempts. By default failed job attempts are destroyed after about a month.
- 1.6.0: Renamed locked_until to locked_at. We now store when we start a given job instead of how long it will be locked by the worker. This allows us to get a reading on how long a job took to execute.
- 1.5.0: Job runners can now be run in parallel. Two new database columns are needed: locked_until and locked_by. This allows us to use pessimistic locking instead of relying on row level locks. This enables us to run as many worker processes as we need to speed up queue processing.
- 1.2.0: Added #send_later to Object for simpler job creation
- 1.0.0: Initial release