title: Drupal difference between DatabaseQueue and BatchQueue
body: <p>Looking at the <a href="https://api.drupal.org/api/drupal/core!core.api.php/group/queue/8.2.x" rel="nofollow noreferrer">Drupal queue documentation</a> it is not clear what the difference is between a <a href="https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Queue%21DatabaseQueue.php/class/DatabaseQueue/8.2.x" rel="nofollow noreferrer">DatabaseQueue</a> and a <a href="https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Queue%21Batch.php/class/Batch/8.2.x" rel="nofollow noreferrer">BatchQueue</a>? Are both FIFO? Will they expire? Serial meaning not concurrent processing?</p>