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Job Runner

These recommendations are for high-volume journal, press or preprint services. Low-volume services can use the built-in job runner with no configuration.

Each application makes use of a jobs queue to handle long-running tasks. Jobs are used to send bulk email notifications, compile statistics, deposit DOIs, update the search index, and more.

On a high-volume site, these tasks may slow down the server while they are being completed. To solve this problem, server administrators can move these tasks to separate requests or even into separate threads on the server.

Most sites will get by without too many problems by using a cron job or the built-in job runner. However, the larger your site is, the more risk there is of jobs causing the site to suddenly slow down during peak periods of activity. In such circumstances, it will be more important to configure the job runner well.

How to Run Jobs #

Every server should be configured with one of the following methods for running jobs: workers, cron, or the built-in job runner. Enabling two methods will not improve the site’s performance.

Workers #

For large sites, we recommend using a worker to process jobs. The worker, when run as a daemon, will wait for jobs to be dispatched and then run them one-by-one in a separate process on the server. When run this way, system resources can be allocated to the worker so that it will not cause spikes in resource usage that slow down the main site.

The following command can be used to initialize a worker.

php lib/pkp/tools/jobs.php work

This command supports most of the options supported by Laravel’s queue:work. Pass the --help flag to learn more.

php lib/pkp/tools/jobs.php work --help

In a production environment, you should use a process monitor like Supervisor to make sure the process stays up and running. Supervisor can be installed on Linux with the following command.

sudo apt-get install supervisor

Create a config file for supervisor, usually located at /etc/supervisor/conf.d.

command=<path-to-php>/php /<root>/lib/pkp/tools/jobs.php work

Replace the following variables in the configuration above with the correct paths in your system:

Variable Description
<path-to-php> Absolute path on the server to the CLI PHP executable. This can be found on most Linux servers by running which php.
<root> Absolute path to the root directory of the application (OJS, OMP, OPS).
<log-file> Absolute path to a log file. If hosting in a cloud environment, you may want to direct logs to stdout.

Restart Supervisor.

sudo service supervisor restart

You may need to run the following command to apply the configuration changes.

supervisorctl reread

To configure Supervisor on other systems, or to learn more about monitoring processes, read the Supervisor documentation.

Once you have set up the worker, turn the default job runner off in config.inc.php:

job_runner = Off

Cron #

A cron job can be configured to process jobs at regular intervals, for example every 30 or 60 seconds.

A cron job configured to run the following command will process all jobs in the queue.

php lib/pkp/tools/jobs.php run

A cron job configured to run the following command will process only one job.

php lib/pkp/tools/jobs.php run --once

Whether or not to process one or all jobs will depend on your environment. When running all jobs at once, a sudden batch of large, resource-intensive jobs could slow down your server. That’s because the cron job will try to churn through everything all at once.

When running one job at a time, the cron job will be less likely to consume a lot of server resources all at once. However, there is a risk that jobs will back up over time. If a bulk email is sent to 5,000 users, it may create 100 jobs. Processing one job every 60 seconds, it would take 100 minutes to send the email.

Once you have set up a cron job, turn the default job runner off in config.inc.php:

job_runner = Off

We recommend using workers for large sites. Learn more about how to monitor jobs to make sure they are not backing up.

Built-in Job Runner #

In some server environments, you may not have permission to configure workers or cron jobs. On these servers, the built-in job runner can be used to process jobs.

The built-in job runner works by running jobs off the back of user requests to the server. When no one visits your site, no jobs are run. As a result, there is a greater risk of jobs causing sudden spikes in resource usage, which will result in delays loading the site.

Turn the built-in job runner on in the config.inc.php file.

job_runner = On

To prevent the server’s resources from being exhausted or hitting the server’s execution timeouts, you can configure the built-in job runner with the following settings.

; The maximum number of jobs to run in a single request when using
; the built-in job runner.
job_runner_max_jobs = 30

; The maximum number of seconds the built-in job runner should spend
; running jobs in a single request.
; This should be less than the max_execution_time the server has
; configured for PHP.
; Lower this setting if jobs are failing due to timeouts.
job_runner_max_execution_time = 30

; The maximum consumerable memory that should be spent by the built-in
; job runner when running jobs.
; Set as a percentage, such as 80%:
; job_runner_max_memory = 80
; Or set as a fixed value in megabytes:
; job_runner_max_memory = 128M
; When setting a fixed value in megabytes, this should be less than the
; memory_limit the server has configured for PHP.
job_runner_max_memory = 80

We recommend staying within the default limits above, unless you know your server is capable of running with higher limits.

How to Monitor Jobs #

You can monitor pending and failed jobs through the CLI tool or the administration interface of the application.

Run the following command to view pending jobs in the terminal.

php lib/pkp/tools/jobs.php list

Or view them in the administration interface by going to Administration > Jobs.

Run the following command to view failed jobs in the terminal.

php lib/pkp/tools/jobs.php failed

Or view them in the administration interface by going to Administration > Failed Jobs. From the admin interface you can also retry failed jobs.

Add the following setting to config.inc.php to automatically delete failed jobs after a certain period.

; Remove failed jobs from the database after the following number of days.
; Remove this setting to leave failed jobs in the database.
delete_failed_jobs_after = 180

Custom Drivers #

Laravel Queues are used to dispatch and process jobs. By default, the application uses the database driver to store and process jobs.

Custom drivers exist for handling jobs with Redis, Beanstalkd, and Amazon SQS. These drivers are not officially supported, but may be implemented with a little coding.

If you use a custom driver, please share your findings with our community.

Troubleshooting #

The best way to troubleshoot failed jobs is through Administration > Failed Jobs in the application. The failed jobs table will provide information on what jobs failed, when, and with what exceptions.

Jobs should never be run while the site is under maintenance, for example during an upgrade.

Learn more about handling user accounts.