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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 Admin Area > Monitoring > Background Jobs (/admin/background_jobs) in GitLab.

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
```

Queue selector (experimental)

Introduced in GitLab Starter 12.8.

CAUTION: Caution: As this is marked as experimental, it is subject to change at any time, including breaking backwards compatibility. This is so that we can react to changes we need for our GitLab.com deployment. We have a tracking issue open to remove the experimental designation from this feature; please comment there if you are interested in using this in your own deployment.

In addition to selecting queues by name, as above, the experimental_queue_selector option allows queue groups to be selected in a more general way using the following components:

Attributes that can be selected.
Operators used to construct a query.

Available attributes

From the list of all available attributes, experimental_queue_selector allows selecting of queues by the following attributes:

feature_category - the GitLab feature category the queue belongs to. For example, the merge queue belongs to the source_code_management category.
has_external_dependencies - whether or not the queue connects to external services. For example, all importers have this set to true.
latency_sensitive - whether or not the queue is particularly sensitive to latency, which also means that its jobs should run quickly. For example, the authorized_projects queue is used to refresh user permissions, and is latency sensitive.
name - the queue name. The other attributes are typically more useful as they are more general, but this is available in case a particular queue needs to be selected.
resource_boundary - if the worker is bound by cpu, memory, or unknown. For example, the project_export queue is memory bound as it has to load data in memory before saving it for export.

Both has_external_dependencies and latency_sensitive are boolean attributes: only the exact string true is considered true, and everything else is considered false.

Available operators

experimental_queue_selector supports the following operators, listed from highest to lowest precedence:

| - the logical OR operator. For example, query_a|query_b (where query_a and query_b are queries made up of the other operators here) will include queues that match either query.
& - the logical AND operator. For example, query_a&query_b (where query_a and query_b are queries made up of the other operators here) will only include queues that match both queries.
!= - the NOT IN operator. For example, feature_category!=issue_tracking excludes all queues from the issue_tracking feature category.
= - the IN operator. For example, resource_boundary=cpu includes all queues that are CPU bound.
, - the concatenate set operator. For example, feature_category=continuous_integration,pages includes all queues from either the continuous_integration category or the pages category. This example is also possible using the OR operator, but allows greater brevity, as well as being lower precedence.

The operator precedence for this syntax is fixed: it's not possible to make AND have higher precedence than OR.

Example queries

In /etc/gitlab/gitlab.rb:

sidekiq_cluster['enable'] = true
sidekiq_cluster['experimental_queue_selector'] = true
sidekiq_cluster['queue_groups'] = [
  # Run all non-CPU-bound queues that are latency sensitive
  'resource_boundary!=cpu&latency_sensitive=true',
  # Run all continuous integration and pages queues that are not latency sensitive
  'feature_category=continuous_integration,pages&latency_sensitive=false'
]

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.

Managing concurrency

When setting the maximum concurrency, keep in mind this normally should not exceed the number of CPU cores available. The values in the examples below are arbitrary and not particular recommendations.

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.

When running a single Sidekiq process (default)

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

This will set the concurrency (number of threads) for the Sidekiq process.

When running Sidekiq cluster

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

sidekiq_cluster['min_concurrency'] = 15
sidekiq_cluster['max_concurrency'] = 25

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

min_concurrency and max_concurrency are independent; one can be set without the other. Setting min_concurrency to 0 will disable the limit.

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

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.

If min_concurrency is equal to max_concurrency, then this value will be used regardless of the number of queues.

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

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.

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