You can see the problem from looking at the code, but it actually created severe problems for real life Hive user.
When alter table has cascade option it does the following:
So it walks all partitions (and this may be huge list) and does some non-trivial operations in one single uber-transaction.
When DbNotificationListener is enabled, it adds an event for each partition, all while
holding a row lock on NOTIFICATION_SEQUENCE table. As a result, while this is happening no other write DDL can proceed. This can sometimes cause DB lock timeouts which cause HMS level operation retries which make things even worse.
In one particular case this pretty much made HMS unusable.