/**
 * Implements hook_entity_update().
 */
function {{ machine_name }}_entity_update($entity, $type) {
  // Update the entity's entry in a fictional table of all entities.
  $info = entity_get_info($type);
  list($id) = entity_extract_ids($type, $entity);
  db_update('example_entity')
    ->fields(array(
      'updated' => REQUEST_TIME,
    ))
    ->condition('type', $type)
    ->condition('id', $id)
    ->execute();
}