Schedule background migration

db/post_migrate/20180916014356_populate_external_pipeline_source.rb

+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class PopulateExternalPipelineSource < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+  MIGRATION = 'PopulateExternalPipelineSource'.freeze
+  BATCH_SIZE = 500
+
+  disable_ddl_transaction!
+
+  class Pipeline < ActiveRecord::Base
+    include EachBatch
+    self.table_name = 'ci_pipelines'
+  end
+
+  def up
+    Pipeline.where(source: nil).tap do |relation|
+      queue_background_migration_jobs_by_range_at_intervals(relation,
+                                                            MIGRATION,
+                                                            5.minutes,
+                                                            batch_size: BATCH_SIZE)
+    end
+  end
+
+  def down
+    # noop
+  end
+end