MySQL is a RDBMS. Or at least that's what it's creators claim it to be.
There's no other self respecting database who's only engine that implements transactions (innoDB) is not created by MySQL guys. Only until recently their own engine claims to support them. Even small in-process databases like Hypersonic and Derby fully support transactions from version one. Flawlessly.
Today I found one more reason for which I think MySQL should not be put under the category RDBMS:
Until recently the maximum was only 31 table. A major WTF?!
I would gladly bet that Hypersonic and Derby do not have a constraint like that (haven't investigated it though).
The stack trace is intently complete to show that this comes from Hibernate. This can be reproduced by having a rich object model with EAGER fetching.
Maybe I'll write a little more on the EAGER fetching and the issues I have: here.