After upgrading from 2.4.6 to OpenDJ 2.6.0 I got the following error:
The JE database contained 2000 entries which had been subjected to a sustained modrate, and is unusable afterward the upgrade. I had thought that this was due to
OPENDJ-752 (FS write barriers) but I am now pretty certain that it is not. Note as well that sometimes the error does not occur immediately on startup, but occur later on: I managed to reproduce it a second time by running modrate on the "upgraded" database.
The reason why I don't think that this has anything to do with
OPENDJ-752 is that I am able to perform multiple cycles of start, modrate, stop, start... against OpenDJ 2.4 or 2.6 without encountering any problems: the issue only occurs after transitioning from 2.4 to 2.6.
I also tried to run the JE DB pre-upgrade tool on a backend once I had hit the issue, but this failed to help. I need to check whether running the JE pre-upgrade tool prevents the problem from occurring.
In my opinion, this issue is a 2.6 blocker, although I have marked it only as critical since there is often a workaround such as reinitialization.