Multiple Hibernate envers FirstLevelCache instances

Question

I have been debugging some strange envers behaviour in my code for a couple of days and have stumbled on something that surprised me. I have confirmed that this is not contributing to my problem but I thought that it would be worth checking my assumptions anyway.

If I get the current Hibernate session in multiple places in a single thread (I am using thread session context) I will always get the same session and therefore I will hit the same level one cache.

I had assumed similar behaviour with envers when getting an audit reader instance. I am using AuditReader reader = AuditReaderFactory.get(session); to get AuditReader instances. I noticed that every time this is called (even within the same session context) I get a new audit reader instance, containing a unique first level cache instance.

It looks like this would result, at best, in the performance hit of multiple, possibly overlapping caches.

I had assumed that, for a session context, I would always get the same AuditReader instance and therefore, a single first level cache. I cannot think of a reason why this would not be the case.

This leaves me with four possibilities:

1. I am not using the correct method to get a session context's audit reader
2. There is a good reason for having multiple audit reader instances
3. There is a bug somewhere in the depths of envers
4. It does not make sense to reuse audit reader instances.

Can someone please provide some insight on this.

Thanks.

Answer 1

If you look at the implementation of AuditReaderFactory (here), a new instance of an AuditReaderImpl is created on each call; the instances are not cached anywhere themselves.

It isn't also specified anywhere that you should get the same instance given the same session; so your request can be treated as a "feature request", but I wouldn't say it's a bug.

There's no specific reason not to reuse same audit reader instances.