Just in case anyone is interested ....
We are making very light use of Jackrabbit 1.5.3 with OCM in our environment.
1. We tripped over an issue whereby DatabasePersistenceManager.java keeps an uncommitted transaction open at all times. I had a rummage around JIRA but I couldn't find anything similar reported.
I couldn't track down the missing commit, so my workaround was to simply patch it to non-transactional behavior (using JDBC auto-commit), and this works fine in our environment including stress testing our use of Jackrabbit, but we're not using features like versioning which may depend on real transactional semantics.
2. We found that OCM-5 was causing a noticeable memory leak in our environment, and the patch suggested in the ticket does fix it.
Is Jackrabbit OCM still a live project? There doesn't seem to have been much activity since the refactor for Jackrabbit 1.6.0