Run multiple Sidekiq processes

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GitLab allows you to start multiple Sidekiq processes to process background jobs at a higher rate on a single instance. By default, Sidekiq starts one worker process and only uses a single core.

NOTE: The information in this page applies only to Linux package installations.

Start multiple processes

When starting multiple processes, the number of processes should at most equal (and not exceed) the number of CPU cores you want to dedicate to Sidekiq. The Sidekiq worker process uses no more than one CPU core.

To start multiple processes, use the sidekiq['queue_groups'] array setting to specify how many processes to create using sidekiq-cluster and which queues they should handle. Each item in the array equates to one additional Sidekiq process, and values in each item determine the queues it works on. In the vast majority of cases, all processes should listen to all queues (see processing specific job classes for more details).

For example, to create four Sidekiq processes, each listening to all available queues:

Edit /etc/gitlab/gitlab.rb:
```
sidekiq['queue_groups'] = ['*'] * 4
```
Save the file and reconfigure GitLab:
```
sudo gitlab-ctl reconfigure
```

To view the Sidekiq processes in GitLab:

On the left sidebar, at the bottom, select Admin.
Select Monitoring > Background jobs.

Concurrency

By default each process defined under sidekiq starts with a number of threads that equals the number of queues, plus one spare thread, up to a maximum of 50. For example, a process that handles all queues uses 50 threads by default.

These threads run inside a single Ruby process, and each process can only use a single CPU core. The usefulness of threading depends on the work having some external dependencies to wait on, like database queries or HTTP requests. Most Sidekiq deployments benefit from this threading.

Manage thread counts explicitly

The correct maximum thread count (also called concurrency) depends on the workload. Typical values range from 5 for highly CPU-bound tasks to 15 or higher for mixed low-priority work. A reasonable starting range is 15 to 25 for a non-specialized deployment.

The values vary according to the work each specific deployment of Sidekiq does. Any other specialized deployments with processes dedicated to specific queues should have the concurrency tuned according to:

The CPU usage of each type of process.
The throughput achieved.

Each thread requires a Redis connection, so adding threads may increase Redis latency and potentially cause client timeouts. See the Sidekiq documentation about Redis for more details.

Manage thread counts with concurrency field

Introduced in GitLab 16.9.

In GitLab 16.9 and later, you can set the concurrency by setting concurrency. This value explicitly sets each process with this amount of concurrency.

For example, to set the concurrency to 20:

Edit /etc/gitlab/gitlab.rb:
```
sidekiq['concurrency'] = 20
```
Save the file and reconfigure GitLab:
```
sudo gitlab-ctl reconfigure
```

Manage thread counts with `min_concurrency` and `max_concurrency` fields (deprecated)

WARNING: The min_concurrency and max_concurrency settings were deprecated in GitLab 16.9 and are planned for removal in 17.0. Use concurrency instead.

We only recommend setting explicit concurrency by setting min_concurrency and max_concurrency to the same value. The two distinct settings are kept for backward compatibility reasons. For more predictable results, use the same values, or you might run into issues with Sidekiq jobs piling up.

For example, to set the concurrency to 20:

Edit /etc/gitlab/gitlab.rb:

sidekiq['min_concurrency'] = 20
sidekiq['max_concurrency'] = 20

Save the file and reconfigure GitLab:
```
sudo gitlab-ctl reconfigure
```

min_concurrency and max_concurrency are independent; one can be set without the other. Setting min_concurrency to 0 disables the limit. Not explicitly setting min_concurrency is the same as setting it to 0.

For each queue group, let N be one more than the number of queues. The concurrency is set to:

min_concurrency, if it's equal to max_concurrency.
N, if it's between min_concurrency and max_concurrency.
max_concurrency, if N exceeds this value.
min_concurrency, if N is less than this value.

When min_concurrency is greater than max_concurrency, it is treated as being equal to max_concurrency.

Modify the check interval

To modify the Sidekiq health check interval for the additional Sidekiq processes:

Edit /etc/gitlab/gitlab.rb:
```
sidekiq['interval'] = 5
```
The value can be any integer number of seconds.
Save the file and reconfigure GitLab:
```
sudo gitlab-ctl reconfigure
```

Troubleshoot using the CLI

WARNING: It's recommended to use /etc/gitlab/gitlab.rb to configure the Sidekiq processes. If you experience a problem, you should contact GitLab support. Use the command line at your own risk.

For debugging purposes, you can start extra Sidekiq processes by using the command /opt/gitlab/embedded/service/gitlab-rails/bin/sidekiq-cluster. This command takes arguments using the following syntax:

/opt/gitlab/embedded/service/gitlab-rails/bin/sidekiq-cluster [QUEUE,QUEUE,...] [QUEUE, ...]

The --dryrun argument allows viewing the command to be executed without actually starting it.

Each separate argument denotes a group of queues that have to be processed by a Sidekiq process. Multiple queues can be processed by the same process by separating them with a comma instead of a space.

Instead of a queue, a queue namespace can also be provided, to have the process automatically listen on all queues in that namespace without needing to explicitly list all the queue names. For more information about queue namespaces, see the relevant section in the Sidekiq development documentation.

Monitor the `sidekiq-cluster` command

The sidekiq-cluster command does not terminate once it has started the desired amount of Sidekiq processes. Instead, the process continues running and forwards any signals to the child processes. This allows you to stop all Sidekiq processes as you send a signal to the sidekiq-cluster process, instead of having to send it to the individual processes.

If the sidekiq-cluster process crashes or receives a SIGKILL, the child processes terminate themselves after a few seconds. This ensures you don't end up with zombie Sidekiq processes.

This allows you to monitor the processes by hooking up sidekiq-cluster to your supervisor of choice (for example, runit).

If a child process died the sidekiq-cluster command signals all remaining process to terminate, then terminate itself. This removes the need for sidekiq-cluster to re-implement complex process monitoring/restarting code. Instead you should make sure your supervisor restarts the sidekiq-cluster process whenever necessary.

PID files

The sidekiq-cluster command can store its PID in a file. By default no PID file is written, but this can be changed by passing the --pidfile option to sidekiq-cluster. For example:

/opt/gitlab/embedded/service/gitlab-rails/bin/sidekiq-cluster --pidfile /var/run/gitlab/sidekiq_cluster.pid process_commit

Keep in mind that the PID file contains the PID of the sidekiq-cluster command and not the PIDs of the started Sidekiq processes.

Environment

The Rails environment can be set by passing the --environment flag to the sidekiq-cluster command, or by setting RAILS_ENV to a non-empty value. The default value can be found in /opt/gitlab/etc/gitlab-rails/env/RAILS_ENV.