Add migration progress checker

ee/db/post_migrate/20181204040404_migrate_project_approvers.rb

@@ -16,7 +16,10 @@ class MigrateProjectApprovers < ActiveRecord::Migration[5.0]
     Project.each_batch(of: BATCH_SIZE) do |scope, _|
       jobs << ['MigrateApproverToApprovalRulesInBatch', ['Project', scope.pluck(:id)]]
     end
-    BackgroundMigration.bulk_perform_async(jobs)
+    BackgroundMigrationWorker.bulk_perform_async(jobs)
+
+    check_time = Gitlab::BackgroundMigration::MigrateApproverToApprovalRulesCheckProgress::RESCHEDULE_DELAY
+    BackgroundMigrationWorker.bulk_perform_in(check_time, [['MigrateApproverToApprovalRulesCheckProgress']])
   end
 
   def down

ee/lib/gitlab/background_migration/migrate_approver_to_approval_rules_check_progress.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    class MigrateApproverToApprovalRulesCheckProgress
+      RESCHEDULE_DELAY = 1.day
+
+      def perform
+        if remaining('MergeRequest') == 0 && remaining('Project') == 0
+          Feature.enable(:approval_rule)
+        else
+          BackgroundMigrationWorker.perform_in(RESCHEDULE_DELAY, self.class.name)
+        end
+      end
+
+      private
+
+      def remaining(class_name)
+        target_type = ActiveRecord::Base.connection.quote(class_name)
+
+        sql_old_schema = <<-SQL.strip_heredoc
+          SELECT count(*) FROM (
+            SELECT target_id FROM "approvers" WHERE "approvers"."target_type" = #{target_type}
+            UNION
+            SELECT target_id FROM "approver_groups" WHERE "approver_groups"."target_type" = #{target_type}
+          ) AS target_count
+        SQL
+
+        sql_new_schema = <<-SQL.strip_heredoc
+          SELECT count(distinct #{class_name.foreign_key}) from approval_#{class_name.underscore}_rules
+        SQL
+
+        count(sql_old_schema) - count(sql_new_schema)
+      end
+
+      def count(sql)
+        ActiveRecord::Base.connection.exec_query(sql).first['count']
+      end
+    end
+  end
+end

ee/spec/migrations/migrate_project_approvers_spec.rb

@@ -13,6 +13,7 @@ describe MigrateProjectApprovers, :migration do
     let(:approval_project_rules) { table(:approval_project_rules) }
     let(:approval_project_rules_users) { table(:approval_project_rules_users) }
     let(:users) { table(:users) }
+    let(:features) { table(:features) }
 
     before do
       namespaces.create(id: 1, name: 'gitlab-org', path: 'gitlab-org')
@@ -35,6 +36,7 @@ describe MigrateProjectApprovers, :migration do
 
       expect(approval_project_rules_users.where(approval_project_rule_id: rule_ids.first).pluck(:user_id)).to contain_exactly(1)
       expect(approval_project_rules_users.where(approval_project_rule_id: rule_ids.last).pluck(:user_id)).to contain_exactly(2)
+      expect(features.where(key: 'approval_rule').exists?).to eq(true)
     end
   end
 end