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expand readme to include more hints

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commit ad27c3e36fd951abb67545e7b711e5ed9521ec79 1 parent dbc5e37
@dmag dmag authored
Showing with 38 additions and 9 deletions.
  1. +38 −9 README.textile
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47 README.textile
@@ -17,17 +17,40 @@ h2. Setup
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.integer :priority, :default => 0 # Allows some jobs to jump to the front of the queue
+ table.integer :attempts, :default => 0 # Provides for retries, but still fail eventually.
+ table.text :handler # YAML-encoded string of the object that will do work
+ table.string :last_error # reason for last failure (See Note below)
+ table.datetime :run_at # When to run. Could be Time.now for immediately, or sometime in the future.
+ table.datetime :locked_at # Set when a client is working on this object
+ table.datetime :failed_at # Set when all retries have failed (actually, by default, the record is deleted instead)
+ table.string :locked_by # Who is working on this object (if locked)
table.timestamps
end
-
+
+On failure, the job is scheduled again in 5 seconds + N ** 4, where N is the number of retries.
+
+The default MAX_ATTEMPTS is 25. After this, the job either deleted (default), or left in the database with "failed_at" set.
+With the default of 25 attempts, the last retry will be 20 days later, with the last interval being almost 100 hours.
+
+The default MAX_RUN_TIME is 4.hours. If your job takes longer than that, another computer could pick it up. It's up to you to
+make sure your job doesn't exceed this time. You should set this to the longest time you think the job could take.
+
+By default, it will delete failed jobs (and it always deletes successful jobs). If you want to keep failed jobs, set
+Delayed::Job.destroy_failed_jobs = false. The failed jobs will be marked with non-null failed_at.
+
+Here is an example of changing job parameters in Rails:
+
+ # config/initializers/delayed_job_config.rb
+ Delayed::Job.destroy_failed_jobs = false
+ silence_warnings do
+ Delayed::Job.const_set("MAX_ATTEMPTS", 3)
+ Delayed::Job.const_set("MAX_RUN_TIME", 5.minutes)
+ end
+
+Note: If your error messages are long, consider changing last_error field to a :text instead of a :string (255 character limit).
+
+
h2. Usage
Jobs are simple ruby objects with a method called perform. Any object which responds to perform can be stuffed into the jobs table.
@@ -64,6 +87,12 @@ You can also run by writing a simple @script/job_runner@, and invoking it extern
Delayed::Worker.new.start
</code></pre>
+Workers can be running on any computer, as long as they have access to the database and their clock is in sync. You can even
+run multiple workers on per computer, but you must give each one a unique name. (TODO: put in an example)
+Keep in mind that each worker will check the database at least every 5 seconds.
+
+Note: The rake task will exit if the database has any network connectivity problems.
+
h3. Cleaning up
You can invoke @rake jobs:clear@ to delete all jobs in the queue.
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