Merge branch '323626-update-doc-for-redis-total' into 'master'

Update doc for redis-total

See merge request gitlab-org/gitlab!72999

doc/development/service_ping/implement.md

@@ -555,13 +555,18 @@ We can also disable tracking completely by using the global flag:
 
 ##### Known events are added automatically in Service Data payload
 
-All events added in [`known_events/common.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/usage_data_counters/known_events/common.yml) are automatically added to Service Data generation under the `redis_hll_counters` key. This column is stored in [version-app as a JSON](https://gitlab.com/gitlab-services/version-gitlab-com/-/blob/master/db/schema.rb#L209).
+Service Ping adds all events [`known_events/*.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/usage_data_counters/known_events) to Service Data generation under the `redis_hll_counters` key. This column is stored in [version-app as a JSON](https://gitlab.com/gitlab-services/version-gitlab-com/-/blob/master/db/schema.rb#L209).
 For each event we add metrics for the weekly and monthly time frames, and totals for each where applicable:
 
 - `#{event_name}_weekly`: Data for 7 days for daily [aggregation](#add-new-events) events and data for the last complete week for weekly [aggregation](#add-new-events) events.
 - `#{event_name}_monthly`: Data for 28 days for daily [aggregation](#add-new-events) events and data for the last 4 complete weeks for weekly [aggregation](#add-new-events) events.
 
-Redis HLL implementation calculates automatic total metrics, if there are more than one metric for the same category, aggregation, and Redis slot.
+Redis HLL implementation calculates total metrics when both of these conditions are met:
+
+- The category is manually included in [CATEGORIES_FOR_TOTALS](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/usage_data_counters/hll_redis_counter.rb#L21).
+- There is more than one metric for the same category, aggregation, and Redis slot.
+
+We add total unique counts for the weekly and monthly time frames where applicable:
 
 - `#{category}_total_unique_counts_weekly`: Total unique counts for events in the same category for the last 7 days or the last complete week, if events are in the same Redis slot and we have more than one metric.
 - `#{category}_total_unique_counts_monthly`: Total unique counts for events in same category for the last 28 days or the last 4 complete weeks, if events are in the same Redis slot and we have more than one metric.