back-hdb backends from OpenLDAP as well as BerkeleyDB from numerous other pieces of software. It has already been noted that back-bdb/hdb are deprecated and that the supported primary database backend going forward from that point was back-mdb.But if the license is the only problem, users still could use an older version ("last good") of BDB. To me I always had the impression that you want to push MDB, not because it's better, but because it's yours. Personally I think users should be able to decide which database they prefer. Ironically many users are using Oracle databases, because some software vendors don't leave customers a choice...
And that is what has been done for all of the OpenLDAP 2.4 series. Keep in mind that this license change is over 6 years old. Additionally, the OpenLDAP project has a very long history of updating what backends are supported to move with times and technology.
With OpenLDAP 2.0, the primary backend was back-ldbm. OpenLDAP 2.1 introduced the back-bdb backend, which was a significant step up from back-ldbm. I helped pioneer the usage of back-bdb in a large scale production environment when I worked for Stanford University back around 2002. OpenLDAP 2.2 introduced back-hdb, and again I helped pioneer its usage in a large scale production environment as part of my job at Stanford.
I also helped test the initial iterations of syncrepl in OpenLDAP 2.2 (which was definitely not ready to be a replacement for slurpd at that time), and similarly did that with the rewrite of syncrepl for OpenLDAP 2.3. Delta-syncrepl was specifically devised because of the issues I hit with syncrepl in OpenLDAP 2.3.
Back-bdb was already deprecated going into OpenLDAP 2.4, and the license changes by Oracle forced everyone's hand into looking for replacement solutions. While I as at Zimbra, I again spearheaded the use of back-lmdb in large scale production environments. I.e., this is simply a part of a the continuous history of the OpenLDAP project adapting its technologies to what is best available.
There is no good reason to keep support for back-bdb or back-hdb at this point, regardless of the license change. They simply do not offer the read or write performance that back-lmdb offers, and they require significant and extensive tuning to even be remotely usable in even a medium scale deployment of few 100k entries. However, the fact that the license did change over 6 years ago has only hastened the inevitable.
Regards, Quanah -- Quanah Gibson-Mount Product Architect Symas Corporation Packaged, certified, and supported LDAP solutions powered by OpenLDAP: <http://www.symas.com>