code: def perform(self):
          
          db_versions = self.table.versions()
  
          version = self.version
          if (version.is_processed(db_versions) and
                  not self.config.force_version == self.version.number):
              self.log(
                  u'version {} is already installed'.format(version.number)
              )
              return
  
          self.start()
          try:
              self._perform_version(version)
          except Exception:
              if sys.version_info < (3, 4):
                  msg = traceback.format_exc().decode('utf8', errors='ignore')
              else:
                  msg = traceback.format_exc()
              error = u'\n'.join(self.logs + [u'\n', msg])
              self.table.record_log(version.number, error)
              raise
          self.finish()
docs: Perform the version upgrade on the database.