doctrine2/manual/docs/en/connection-management/lazy-connecting-to-database.txt

Lazy-connecting to database can save a lot of resources. There might be many pages where you don't need an actual database connection, hence its always recommended to use lazy-connecting (that means Doctrine will only connect to database when needed).

This feature can be very useful when using for example page caching, hence not actually needing a database connection on every request. Remember connecting to database is an expensive operation.

<code type="php">
$dsn = 'mysql://username:password@localhost/test';

// initalize a new Doctrine_Connection
$conn = Doctrine_Manager::connection($dsn);
// !! no actual database connection yet !!

// connects database and performs a query
$conn->query('FROM User u');
</code>