Metrics: Delete models & database tables/columns

Overview

⚠️ Removal should take place during %16.0.

⚠️ Category:Metrics code is intertwined with the metrics GitLab reports on itself. Only Category:Metrics should be removed. Similarly, some items named like PrometheusAlert are also used for AlertManagement::Alert and should not be removed.

As part of Monitor: Metrics Deprecation and Removal (&10107 - closed), we want to delete all models & data corresponding the Metrics Dashboard part of Category:Metrics.

Implementation plan

1. Identify all data used exclusively for Category:Metrics
2. Add ignore rules for the relevant columns in %16.0
3. Delete all model files for the relevant tables %16.0
4. Drop tables in a post-migrate migration %16.0
5. Drop relevant columns in %16.1
6. Remove ignore rules for columns in %16.2

Relevant processes to follow

• Migration style guide for dropping tables
• Guide for dropping columns
• Updating the database dictionary

Relevant code

The list below is meant as an aid & may not be exhaustive.

• Models & tables:
  • ProjectMetricsSettings
  • PrometheusMetric
  • PrometheusAlert
  • PrometheusAlertEvent
  • SelfManagedPrometheusAlertEvent
  • Metrics::Dashboard::Annotation
  • Metrics::UsersStarredDashboard
• Tables without models:
  • issues_prometheus_alert_events
  • issues_self_managed_prometheus_alert_events
• Columns:
  • project_features.metrics_dashboard_access_level
  • alert_management_alerts#prometheus_alert_id
• Models without tables:
  • app/models/performance_monitoring/*
  • lib/gitlab/prometheus/* (except internal.rb in scope of gitlab-org/monitor/respond#112 (closed))

NOTE: Don't remove ApplicationSettings#prometheus_metrics_enabled or ResourceStateEvents#close_auto_resolve_prometheus_alert.