split up migrations

db/migrate/20170312114329_add_auto_canceled_by_id_to_pipeline.rb

@@ -21,22 +21,9 @@ class AddAutoCanceledByIdToPipeline < ActiveRecord::Migration
   #
   # To disable transactions uncomment the following line and remove these
   # comments:
-  disable_ddl_transaction!
-
-  def up
-    on_delete =
-      if Gitlab::Database.mysql?
-        :nullify
-      else
-        'SET NULL'
-      end
+  # disable_ddl_transaction!
 
+  def change
     add_column :ci_pipelines, :auto_canceled_by_id, :integer
-    add_concurrent_foreign_key :ci_pipelines, :ci_pipelines, column: :auto_canceled_by_id, on_delete: on_delete
-  end
-
-  def down
-    remove_foreign_key :ci_pipelines, column: :auto_canceled_by_id
-    remove_column :ci_pipelines, :auto_canceled_by_id
   end
 end

db/migrate/20170312114529_add_auto_canceled_by_id_foreign_key_to_pipeline.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddAutoCanceledByIdForeignKeyToPipeline < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  disable_ddl_transaction!
+
+  def up
+    on_delete =
+      if Gitlab::Database.mysql?
+        :nullify
+      else
+        'SET NULL'
+      end
+
+    add_concurrent_foreign_key :ci_pipelines, :ci_pipelines, column: :auto_canceled_by_id, on_delete: on_delete
+  end
+
+  def down
+    remove_foreign_key :ci_pipelines, column: :auto_canceled_by_id
+  end
+end