Kari Mattsson wrote:
If 'D' is the best companion for 'O', it is evolutionary to allow 'O+1' to still work with 'D'.
Requiring 'D+1' with 'O+1' makes upgrades more difficult to arrange as a whole.
So, maybe my point is change management.
As Quanah already said, change management is no different here than it has ever been: slapcat with the old version, slapadd with the new. That has always been the recommended upgrade procedure.
As an aside, the current back-bdb code will still compile and work properly with everything going back to BDB 4.0 (if you can still find a copy of that anywhere). You just have to tell the configure script to skip the version check if you really want to run things that way. But there are plenty of good reasons not to keep using those old BDB releases, which is why we raise the requirements in the configure script.