Count merged MRs using approval rules in Usage Data

Adds metric to report the count of approval rules
for merged merge requests.

db/post_migrate/20201002175953_add_index_for_merged_merge_requests.rb

+# frozen_string_literal: true
+
+class AddIndexForMergedMergeRequests < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_NAME = 'idx_merge_requests_on_merged_state'
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :merge_requests,
+                         :id,
+                         where: 'state_id = 3',
+                         name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :merge_requests, INDEX_NAME
+  end
+end

db/schema_migrations/20201002175953

+619e788f8868a2ff602a06e0025154b0b10b17cd69edcce70378e11750d5e686
\ No newline at end of file

db/structure.sql

@@ -19474,6 +19474,8 @@ CREATE INDEX idx_members_created_at_user_id_invite_token ON members USING btree
 
 CREATE INDEX idx_merge_requests_on_id_and_merge_jid ON merge_requests USING btree (id, merge_jid) WHERE ((merge_jid IS NOT NULL) AND (state_id = 4));
 
+CREATE INDEX idx_merge_requests_on_merged_state ON merge_requests USING btree (id) WHERE (state_id = 3);
+
 CREATE INDEX idx_merge_requests_on_source_project_and_branch_state_opened ON merge_requests USING btree (source_project_id, source_branch) WHERE (state_id = 1);
 
 CREATE INDEX idx_merge_requests_on_state_id_and_merge_status ON merge_requests USING btree (state_id, merge_status) WHERE ((state_id = 1) AND ((merge_status)::text = 'can_be_merged'::text));

ee/changelogs/unreleased/233765_approval_rule_merged_mrs.yml

+---
+title: Count merged MRs using approval rules in usage data
+merge_request: 42911
+author:
+type: added

ee/lib/ee/gitlab/usage_data.rb

@@ -192,6 +192,9 @@ module EE
                 merge_requests_with_optional_codeowners: distinct_count(::ApprovalMergeRequestRule.code_owner_approval_optional, :merge_request_id),
                 merge_requests_with_overridden_project_rules: merge_requests_with_overridden_project_rules,
                 merge_requests_with_required_codeowners: distinct_count(::ApprovalMergeRequestRule.code_owner_approval_required, :merge_request_id),
+                merged_merge_requests_using_approval_rules: count(::MergeRequest.merged.joins(:approval_rules), # rubocop: disable CodeReuse/ActiveRecord
+                                                                  start: merge_request_minimum_id,
+                                                                  finish: merge_request_maximum_id),
                 projects_mirrored_with_pipelines_enabled: count(::Project.mirrored_with_enabled_pipelines),
                 projects_reporting_ci_cd_back_to_github: count(::GithubService.active),
                 status_page_projects: count(::StatusPage::ProjectSetting.enabled),
@@ -398,6 +401,18 @@ module EE
           end
         end
 
+        def merge_request_minimum_id
+          strong_memoize(:merge_request_minimum_id) do
+            ::MergeRequest.minimum(:id)
+          end
+        end
+
+        def merge_request_maximum_id
+          strong_memoize(:merge_request_maximum_id) do
+            ::MergeRequest.maximum(:id)
+          end
+        end
+
         def ldap_config_present_for_any_provider?(configuration_item)
           ldap_available_servers.any? { |server_config| server_config[configuration_item.to_s] }
         end
@@ -465,6 +480,16 @@ module EE
           )
         end
         # rubocop:enable CodeReuse/ActiveRecord
+
+        override :clear_memoized
+        def clear_memoized
+          super
+
+          clear_memoization(:approval_merge_request_rule_minimum_id)
+          clear_memoization(:approval_merge_request_rule_maximum_id)
+          clear_memoization(:merge_request_minimum_id)
+          clear_memoization(:merge_request_maximum_id)
+        end
       end
     end
   end

ee/spec/lib/ee/gitlab/usage_data_spec.rb

@@ -225,6 +225,17 @@ RSpec.describe Gitlab::UsageData do
     end
   end
 
+  describe 'merge requests merged using approval rules' do
+    before do
+      create(:approval_merge_request_rule, merge_request: create(:merge_request, :merged))
+      create(:approval_merge_request_rule, merge_request: create(:merge_request))
+    end
+
+    it 'counts the approval rules for merged merge requests' do
+      expect(described_class.system_usage_data[:counts][:merged_merge_requests_using_approval_rules]).to eq(1)
+    end
+  end
+
   describe '.operations_dashboard_usage' do
     subject { described_class.operations_dashboard_usage }
 
@@ -692,4 +703,22 @@ RSpec.describe Gitlab::UsageData do
       )
     end
   end
+
+  it 'clears memoized values' do
+    values = %i(issue_minimum_id issue_maximum_id
+                project_minimum_id project_maximum_id
+                user_minimum_id user_maximum_id unique_visit_service
+                deployment_minimum_id deployment_maximum_id
+                auth_providers
+                approval_merge_request_rule_minimum_id
+                approval_merge_request_rule_maximum_id
+                merge_request_minimum_id
+                merge_request_maximum_id)
+
+    values.each do |key|
+      expect(described_class).to receive(:clear_memoization).with(key)
+    end
+
+    described_class.uncached_data
+  end
 end

lib/gitlab/usage_data.rb

@@ -816,8 +816,6 @@ module Gitlab
         clear_memoization(:unique_visit_service)
         clear_memoization(:deployment_minimum_id)
         clear_memoization(:deployment_maximum_id)
-        clear_memoization(:approval_merge_request_rule_minimum_id)
-        clear_memoization(:approval_merge_request_rule_maximum_id)
         clear_memoization(:project_minimum_id)
         clear_memoization(:project_maximum_id)
         clear_memoization(:auth_providers)

spec/lib/gitlab/usage_data_spec.rb

@@ -28,9 +28,16 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
                     project_minimum_id project_maximum_id
                     user_minimum_id user_maximum_id unique_visit_service
                     deployment_minimum_id deployment_maximum_id
-                    approval_merge_request_rule_minimum_id
-                    approval_merge_request_rule_maximum_id
                     auth_providers)
+
+        if Gitlab.ee?
+          values << %i(approval_merge_request_rule_minimum_id
+                       approval_merge_request_rule_maximum_id
+                       merge_request_minimum_id
+                       merge_request_maximum_id)
+          values.flatten!
+        end
+
         values.each do |key|
           expect(described_class).to receive(:clear_memoization).with(key)
         end