Upgrade of Hibernate from version 3.0 to 3.6

I'm working on a project which uses Hibernate 3.0(released in 2005), though the project itself is only 4 months old. The catch is we have already written millions of lines of code. We realized we are using Hibernate 3.0 only yesterday and now we badly want to move to the latest stable release 3.6.6.

So I want to know:

• Will there be a lot of changes in the way we map hbm files开发者_开发技巧?(and properties file)
• Are we likely to get major improvement in performance?(currently we are having some performance issues due to Hibernate's badly formed queries)
• Will there be a lot of changes in the way we write HQL?(we are using HQL heavily)

Appreciate your help.

I think you should read Hibernate3 Migration Guides from 3.0 step by step up to 3.6 Hibernate

And here is the quick search in the hibernate changelog about the improvement and path on the performance from 3.0 to 3.6

• [HHH-5823] - Poor multithread performance in UpdateTimestampsCache class
• [HHH-5824] - Poor multithread performance in SessionFactoryImpl.getQueryCache method
• [HHH-3860] - Cascading performance problems when session contains many entities
• [HHH-3357] - improve performance of session.clear()
• [HHH-2553] - New LoadContexts Implementation causing possible performance degradation
• [HHH-2957] - ActionQueue Insertion sort performance degrades exponentially (Jay Erb)
• [HHH-2553] - New LoadContexts Implementation causing possible performance degradation
• [HHH-2229] - Performance issue with fix for HHH-1293, CGLIBLazyInitializer may be slower for certain Java classes
• [HHH-2023] - performance optimization of JTATransactionFactory.isTransactionInProgress()
• [HHH-864] - Use QUERY_CACHE for sessions with filters to improve performance
• [HHH-525] - cglib related startup performance

You can search in the Hibernate JIRA for each item 's details.Good luck