$db->begin();
$db->savepoint('1.0');
$db->savepoint('1.1');
$db->rollback('1.0'); // both savepoints gone

$db->begin('inner');
$db->savepoint('1.0');
$db->savepoint('1.1');
$db->commit() // same as commit('inner')

$db->savepoint('1.0');
$db->savepoint('1.1');

$db->commit() // the real commit