DERBY-4437 attempted to improve the concurrency of identity columns by using SYSSEQUENCE-style sequence generators. These improvements caused NsTest to behave differently than it used to and they disclosed a problem in clearing the identity cache. The community lost confidence in this solution and it was backed out of the 10.8 branch under issue DERBY-5448. This new issue is filed to back the improvements out of the 10.9 trunk. Further useful discussion about how to improve the concurrency and correctness of identity columns has been taking place on DERBY-5443 and DERBY-5493.
For the 10.9 release, identity columns will return to their old behavior of being ill-suited for high concurrency applications. Applications which need higher concurrency should be re-coded to use sequences rather than identity columns.