We are using Hibernate against a legacy DB2/400 database with 1000 tables (the mapping files and POJOs are generated by reverse engineering).

However, creating the SessionFactory takes an excessive amount of time and usually dies with an OutOfMemory error. Now, I'm sure I can get around the mem issues by tuning the -X mem flags, but what are other peoples experiences with Hibernate and very large schemas?

How do you develop with this, if each unit test takes 5 minutes to start?

This discussion might help
http://forums.hibernate.org/viewtopic.php?p=2243331

O, and please make sure that H does not try to create or update DB schema, check value of hibernate.hbm2ddl.auto parameter

Thanks! I will follow up this in the other posting that you mentioned.

Note: it is NOT generating the schema, etc... the loading that it happening is legitimate.

We were able to trim down our Hiberante-mapped data model size to around 500 tables (the other section of the data model is not necessary for our project yet).

I have been able to concentrate on total loading time, etc.. I am using Hiberante behind Spring, with lots of Spring AOP poxies etc. Most of the time was being spent generating the CGLIB proxies for Spring AOP, not for Hiberante.

That being said, it still takes Hibernate around 30s to load 500 tables if I 'run' the app, and it takes around 60s to load if I 'debug' the app. So, the development cycle is very slow since I am always debugging, which takes over 1 minute to start.