Extra Sidekiq processes (STARTER ONLY)

NOTE: Note: The information in this page applies only to Omnibus GitLab.

GitLab Starter allows one to start an extra set of Sidekiq processes besides the default one. These processes can be used to consume a dedicated set of queues. This can be used to ensure certain queues always have dedicated workers, no matter the number of jobs that need to be processed.

Available Sidekiq queues

For a list of the existing Sidekiq queues, check the following files:

Each entry in the above files represents a queue on which extra Sidekiq processes can be started.

Starting extra processes

To start extra Sidekiq processes, you must enable sidekiq-cluster:

Edit /etc/gitlab/gitlab.rb and add:
```
sidekiq_cluster['enable'] = true
```
You will then need to specify how many additional processes to create via sidekiq-cluster and which queue they should handle via the sidekiq_cluster['queue_groups'] array setting. Each item in the array equates to one additional Sidekiq process, and values in each item determine the queues it works on.

For example, the following setting adds additional Sidekiq processes to two queues, one to elastic_indexer and one to mailers:
```
sidekiq_cluster['queue_groups'] = [
  "elastic_indexer",
  "mailers"
]
```
To have an additional Sidekiq process handle multiple queues, add multiple queue names to its item delimited by commas. For example:
```
sidekiq_cluster['queue_groups'] = [
  "elastic_indexer, elastic_commit_indexer",
  "mailers"
]
```
Save the file and reconfigure GitLab for the changes to take effect:
```
sudo gitlab-ctl reconfigure
```

Once the extra Sidekiq processes are added, you can visit the "Background Jobs" section under the admin area in GitLab (/admin/background_jobs).

Negating settings

To have the additional Sidekiq processes work on every queue except the ones you list:

After you follow the steps for starting extra processes, edit /etc/gitlab/gitlab.rb and add:
```
sidekiq_cluster['negate'] = true
```
Save the file and reconfigure GitLab for the changes to take effect:
```
sudo gitlab-ctl reconfigure
```

Ignore all GitHub import queues

When importing from GitHub, Sidekiq might use all of its resources to perform those operations. To set up a separate sidekiq-cluster process to ignore all GitHub import-related queues:

Edit /etc/gitlab/gitlab.rb and add:

sidekiq_cluster['enable'] = true
sidekiq_cluster['negate'] = true
sidekiq_cluster['queue_groups'] = [
  "github_import_advance_stage",
  "github_importer:github_import_import_diff_note",
  "github_importer:github_import_import_issue",
  "github_importer:github_import_import_note",
  "github_importer:github_import_import_lfs_object",
  "github_importer:github_import_import_pull_request",
  "github_importer:github_import_refresh_import_jid",
  "github_importer:github_import_stage_finish_import",
  "github_importer:github_import_stage_import_base_data",
  "github_importer:github_import_stage_import_issues_and_diff_notes",
  "github_importer:github_import_stage_import_notes",
  "github_importer:github_import_stage_import_lfs_objects",
  "github_importer:github_import_stage_import_pull_requests",
  "github_importer:github_import_stage_import_repository"
]

Save the file and reconfigure GitLab for the changes to take effect:
```
sudo gitlab-ctl reconfigure
```

Number of threads

Each process defined under sidekiq_cluster starts with a number of threads that equals the number of queues, plus one spare thread. For example, a process that handles the process_commit and post_receive queues will use three threads in total.

Limiting concurrency

To limit the concurrency of the Sidekiq processes:

Edit /etc/gitlab/gitlab.rb and add:
```
sidekiq_cluster['concurrency'] = 25
```
Save the file and reconfigure GitLab for the changes to take effect:
```
sudo gitlab-ctl reconfigure
```

For each queue group, the concurrency factor will be set to min(number of queues, N). Setting the value to 0 will disable the limit. Keep in mind this normally would not exceed the number of CPU cores available.

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.

Modifying the check interval

To modify the check interval for the additional Sidekiq processes:

Edit /etc/gitlab/gitlab.rb and add:
```
sidekiq_cluster['interval'] = 5
```
Save the file and reconfigure GitLab for the changes to take effect.

This tells the additional processes how often to check for enqueued jobs.

Troubleshooting using the CLI

CAUTION: 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/ee/bin/sidekiq-cluster. This command takes arguments using the following syntax:

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

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 style guide.

For example, say you want to start 2 extra processes: one to process the process_commit queue, and one to process the post_receive queue. This can be done as follows:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit post_receive

If you instead want to start one process processing both queues, you'd use the following syntax:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit,post_receive

If you want to have one Sidekiq process dealing with the process_commit and post_receive queues, and one process to process the gitlab_shell queue, you'd use the following:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit,post_receive gitlab_shell

Monitoring the `sidekiq-cluster` command

The sidekiq-cluster command will not terminate once it has started the desired amount of Sidekiq processes. Instead, the process will continue running and forward any signals to the child processes. This makes it easy to stop all Sidekiq processes as you simply 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 will terminate themselves after a few seconds. This ensures you don't end up with zombie Sidekiq processes.

All of this makes monitoring the processes fairly easy. Simply hook up sidekiq-cluster to your supervisor of choice (e.g. runit) and you're good to go.

If a child process died the sidekiq-cluster command will signal 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/ee/bin/sidekiq-cluster --pidfile /var/run/gitlab/sidekiq_cluster.pid process_commit

Keep in mind that the PID file will contain the PID of the sidekiq-cluster command and not the PID(s) 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.

Using negation

You're able to run all queues in sidekiq_queues.yml file on a single or multiple processes with exceptions using the --negate flag.

For example, say you want to run a single process for all queues, except process_commit and post_receive:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit,post_receive --negate

For multiple processes of all queues (except process_commit and post_receive):

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit,post_receive process_commit,post_receive --negate

Limiting concurrency

By default, sidekiq-cluster will spin up extra Sidekiq processes that use one thread per queue up to a maximum of 50. If you wish to change the cap, use the -m N option. For example, this would cap the maximum number of threads to 1:

/opt/gitlab/embedded/service/gitlab-rails/ee/bin/sidekiq-cluster process_commit,post_receive -m 1

Extra Sidekiq processes (STARTER ONLY)

Available Sidekiq queues

Starting extra processes

Negating settings

Ignore all GitHub import queues

Number of threads

Limiting concurrency

Modifying the check interval

Troubleshooting using the CLI

Monitoring the sidekiq-cluster command

PID files

Environment

Using negation

Limiting concurrency

Monitoring the `sidekiq-cluster` command