doctrine2/manual/new/docs/en/exceptions-and-warnings.txt

++ Manager exceptions

Doctrine_Manager_Exception is thrown if something failed at the connection management

<code type="php">
try {
    $manager->getConnection('unknown');
} catch (Doctrine_Manager_Exception) {
    // catch errors
}
</code>

++ Relation exceptions

Relation exceptions are being thrown if something failed during the relation parsing. 

++ Connection exceptions

Connection exceptions are being thrown if something failed at the database level. Doctrine offers fully portable database error handling. This means that whether you are using sqlite or some other database you can always get portable error code and message for the occurred error.

<code type="php">
try {
    $conn->execute('SELECT * FROM unknowntable');
} catch (Doctrine_Connection_Exception $e) {
    print 'Code : ' . $e->getPortableCode();
    print 'Message : ' . $e->getPortableMessage();
}
</code>

++ Query exceptions

thrown if DQL parsing fails somehow