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---
stage: Growth
group: Product Intelligence
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
---
# Metrics instrumentation guide
This guide describes how to develop Service Ping metrics using metrics instrumentation.
## Nomenclature
- **Instrumentation class**:
- Inherits one of the metric classes: `DatabaseMetric`, `RedisMetric`, `RedisHLLMetric` or `GenericMetric`.
- Implements the logic that calculates the value for a Service Ping metric.
- **Metric definition**
The Service Data metric YAML definition.
- **Hardening**:
Hardening a method is the process that ensures the method fails safe, returning a fallback value like -1.
## How it works
A metric definition has the [`instrumentation_class`](metrics_dictionary.md) field, which can be set to a class.
The defined instrumentation class should have one of the existing metric classes: `DatabaseMetric`, `RedisMetric`, `RedisHLLMetric`, or `GenericMetric`.
Using the instrumentation classes ensures that metrics can fail safe individually, without breaking the entire
process of Service Ping generation.
We have built a domain-specific language (DSL) to define the metrics instrumentation.
## Database metrics
[Example of a merge request that adds a database metric](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60022).
```ruby
module Gitlab
module Usage
module Metrics
module Instrumentations
class CountBoardsMetric < DatabaseMetric
operation :count
relation { Board }
end
end
end
end
end
```
## Redis metrics
[Example of a merge request that adds a `Redis` metric](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/66582).
Count unique values for `source_code_pushes` event.
Required options:
- `event`: the event name.
- `counter_class`: one of the counter classes from the `Gitlab::UsageDataCounters` namespace; it should implement `read` method or inherit it from `BaseCounter`.
```yaml
time_frame: all
data_source: redis
instrumentation_class: 'RedisMetric'
options:
event: pushes
counter_class: SourceCodeCounter
```
## Redis HyperLogLog metrics
[Example of a merge request that adds a `RedisHLL` metric](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/61685).
Count unique values for `i_quickactions_approve` event.
```yaml
time_frame: 28d
data_source: redis_hll
instrumentation_class: 'RedisHLLMetric'
options:
events:
- i_quickactions_approve
```
## Generic metrics
[Example of a merge request that adds a generic metric](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60256).
```ruby
module Gitlab
module Usage
module Metrics
module Instrumentations
class UuidMetric < GenericMetric
value do
Gitlab::CurrentSettings.uuid
end
end
end
end
end
end
```
## Support for instrumentation classes
There is support for:
- `count`, `distinct_count`, `estimate_batch_distinct_count` for [database metrics](#database-metrics).
- [Redis metrics](#redis-metrics).
- [Redis HLL metrics](#redis-hyperloglog-metrics).
- [Generic metrics](#generic-metrics), which are metrics based on settings or configurations.
There is no support for:
- `add`, `sum`, `histogram` for database metrics.
You can [track the progress to support these](https://gitlab.com/groups/gitlab-org/-/epics/6118).
## Create a new metric instrumentation class
To create a stub instrumentation for a Service Ping metric, you can use a dedicated [generator](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/generators/gitlab/usage_metric_generator.rb):
The generator takes the class name as an argument and the following options:
- `--type=TYPE` Required. Indicates the metric type. It must be one of: `database`, `generic`, `redis`.
- `--operation` Required for `database` type. It must be one of: `count`, `distinct_count`, `estimate_batch_distinct_count`.
- `--ee` Indicates if the metric is for EE.
```shell
rails generate gitlab:usage_metric CountIssues --type database
create lib/gitlab/usage/metrics/instrumentations/count_issues_metric.rb
create spec/lib/gitlab/usage/metrics/instrumentations/count_issues_metric_spec.rb
```
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