# GitLab Developers Guide to service measurement

You can enable service measurement in order to debug any slow service's execution time, number of SQL calls, garbage collection stats, memory usage, etc.

## Measuring module

The measuring module is a tool that allows to measure a service's execution, and log:

- Service class name
- Execution time
- Number of SQL calls
- Detailed `gc` stats and diffs
- RSS memory usage
- Server worker ID

The measuring module will log these measurements into a structured log called [`service_measurement.log`](../administration/logs.md#service_measurementlog),
as a single entry for each service execution.

NOTE: **Note:**
For GitLab.com, `service_measurement.log` is ingested in Elasticsearch and Kibana as part of our monitoring solution.

## How to use it

The measuring module allows you to easily measure and log execution of any service,
by just prepending `Measurable` in any Service class, on the last line of the file that the class resides in.

For example, to prepend a module into the `DummyService` class, you would use the following approach:

```ruby
class DummyService
  def execute
  # ...
  end
end

DummyService.prepend(Measurable)
```

In case when you are prepending a module from the `EE` namespace with EE features, you need to prepend Measurable after prepending the `EE` module.

This way, `Measurable` will be at the bottom of the ancestor chain, in order to measure execution of `EE` features as well:

```ruby
class DummyService
  def execute
  # ...
  end
end

DummyService.prepend_if_ee('EE::DummyService')
DummyService.prepend(Measurable)
```

### Log additional attributes

In case you need to log some additional attributes, it is possible to define `extra_attributes_for_measurement` in the service class:

```ruby
def extra_attributes_for_measurement
  {
    project_path: @project.full_path,
    user: current_user.name
  }
end
```

NOTE: **Note:**
Once the measurement module is injected in the service, it will be behind generic feature flag.
In order to actually use it, you need to enable measuring for the desired service by enabling the feature flag.

### Enabling measurement using feature flags

In the following example, the `:gitlab_service_measuring_projects_import_service`
[feature flag](feature_flags/development.md#enabling-a-feature-flag-locally-in-development) is used to enable the measuring feature
for `Projects::ImportService`.

From ChatOps:

```shell
/chatops run feature set gitlab_service_measuring_projects_import_service true
```
