This mirrors the experience I have as well. I (currently) don't know what will cause Hibernate to flush but I certainly do know that I had to know this exactly

This mirrors the experience I have as well. I (currently) don't know what will cause Hibernate to flush but I certainly do know that I had to know this exactly and had to do some really painful debugging at points. The worst one I was on was just early prototyping of an app that used Hibernate and we had so many problems with performance and Hibernate(isms) that the whole thing seemed destined to fail even though our use case was exactly what ORM/Hibernate are for...yet we still have to control when changed flushed because otherwise things would get wonky really quickly.