|By default, on `Model.delete()` Django emulates `ON DELETE CASCADE`. On App Engine this is not possible because queries are disabled while running a transaction. Even without transactions this can be very inefficient on App Engine, SimpleDB, and other NoSQL DBs because Django has to run a lot of queries and retrieve a lot of model instance. Even worse, since this operation is so inefficient it can be absolutely impossible to retrieve all related entities if there are significantly more than 1000 entities (on GAE the 1000 results limit has been removed, but it's still not possible to retrieve e.g. 5000 results).