RQ Job Queues

Pootle makes use of RQ to manage background jobs.

Some tasks are performed using background jobs and we expect more components to use it in future.

The RQ queue is managed by Redis and it is setup in the RQ_QUEUES and CACHES settings.

Running job workers

The queue is processed by Workers. Any number of workers may be started and will process jobs in the default queue. The rqworker command is used to start a Worker.

Monitoring the queue

At the simplest level the Admin dashboard will tell you if the queue is active and how many workers are available to service the queue. It also lists the number of pending jobs and the number of failed jobs. This gives you a quick way to see if anything is wrong.

Working with failed jobs

If a job fails it needs to be investigated. In most cases a traceback will indicate why the job failed.

The simplest way to work with queues and jobs is to use rq-dashboard, though you likely don’t want to deploy that on a production server. With this you can see the jobs in the queue, you can check the tracebacks and you can retry failed jobs.

In the case of a production server you can make use of the following commands to manage jobs:

$ redis-cli -n 2 lrange rq:queue:default 0 -1

This will display all pending job IDs in the default queue. We’re using the Redis DB number 2, the default RQ queue on a standard Pootle install.

$ redis-cli -n 2 lrange rq:queue:failed 0 -1

This will display the failed job IDs.

To investigate a failed job simply add rq:job: prefix to a job ID and use a command such as this:

$ redis-cli -n 2 hgetall rq:job:60ed13df-0ce5-4b98-96f0-f8e0294ba421

This will allow you to see any traceback and investigate and solve them.

To push failed jobs back into the queue we simply run the retry_failed_jobs management command.

Delete all failed jobs

Sometimes failed jobs no longer apply since they refer to removed items, so no matter how many times you run them they will keep failing. Note that sometimes those unrecoverable failed jobs are in company of other failed jobs that can be re-run by using the retry_failed_jobs management command:

(env) $ pootle retry_failed_jobs

In order to delete all the failed jobs you must first stop the workers.

Once the workers are stopped make sure that there are no failed jobs that you don’t want to remove. In case there is any restart the workers to re-run them with retry_failed_jobs. Stop the workers again once those jobs are completed. Check again that all the failed jobs are the ones you want to remove.

In order to perform a bulk delete of all failed jobs run the following commands:

$ redis-cli -n 2 LRANGE "rq:queue:failed" 0 -1 | perl -nE 'chomp; `redis-cli DEL rq:job:$_`;'

Now remove the list of failed jobs:

$ redis-cli -n 2 DEL "rq:queue:failed"

Do not forget to restart the workers.