Add index for project_id on incident issue type

- Update schema

changelogs/unreleased/233719-project-creating-incidents-usage-ping.yml

+---
+title: Add projects_creating_incidents to usage ping counts
+merge_request: 42934
+author:
+type: added

db/migrate/20200927224750_add_incident_issue_type_index_to_issues.rb

+# frozen_string_literal: true
+
+class AddIncidentIssueTypeIndexToIssues < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  INCIDENT_ISSUE_TYPE = 1
+  INDEX_NAME = 'index_issues_project_id_issue_type_incident'
+
+  def up
+    add_concurrent_index :issues, :project_id, where: "issue_type = #{INCIDENT_ISSUE_TYPE}", name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name(:issues, INDEX_NAME)
+  end
+end

db/schema_migrations/20200927224750

+8e0c5be3d6fe2d0d718c7b7a99d84b14dfc6006f780ec0622eb5aae937e6b367
\ No newline at end of file

db/structure.sql

@@ -20372,6 +20372,8 @@ CREATE INDEX index_issues_on_updated_at ON issues USING btree (updated_at);
 
 CREATE INDEX index_issues_on_updated_by_id ON issues USING btree (updated_by_id) WHERE (updated_by_id IS NOT NULL);
 
+CREATE INDEX index_issues_project_id_issue_type_incident ON issues USING btree (project_id) WHERE (issue_type = 1);
+
 CREATE UNIQUE INDEX index_jira_connect_installations_on_client_key ON jira_connect_installations USING btree (client_key);
 
 CREATE INDEX index_jira_connect_subscriptions_on_namespace_id ON jira_connect_subscriptions USING btree (namespace_id);

lib/gitlab/usage_data.rb

@@ -138,6 +138,7 @@ module Gitlab
             pages_domains: count(PagesDomain),
             pool_repositories: count(PoolRepository),
             projects: count(Project),
+            projects_creating_incidents: distinct_count(Issue.incident, :project_id),
             projects_imported_from_github: count(Project.where(import_type: 'github')),
             projects_with_repositories_enabled: count(ProjectFeature.where('repository_access_level > ?', ProjectFeature::DISABLED)),
             projects_with_error_tracking_enabled: count(::ErrorTracking::ProjectErrorTrackingSetting.where(enabled: true)),

spec/lib/gitlab/usage_data_spec.rb

@@ -497,6 +497,7 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
       expect(count_data[:personal_snippets]).to eq(2)
       expect(count_data[:project_snippets]).to eq(4)
 
+      expect(count_data[:projects_creating_incidents]).to eq(2)
       expect(count_data[:projects_with_packages]).to eq(2)
       expect(count_data[:packages]).to eq(4)
       expect(count_data[:user_preferences_user_gitpod_enabled]).to eq(1)