Forum OpenACS Development: Re: OpenACS 5.9 Complaints about PostgreSQL 8.4
The HEAD version of OpenACS is essentially OpenACS 5.8.*. The fact that it does not complain about pg 8.4 says nothing that it works with it. The head version is not a released version (and never was). Currently, all development happens in the oacs-5-9 branch. When active development stops in oacs-5-9, the version will be merged with HEAD. The version numbering of HEAD acs current release + 1 is needed for the apm management.
If some of your installations work with pg 8.4, then remove the check on your installations, but you have to do this on your own risk .... unless there is a volunteer who provides support for pg 8.4.
Thanks for the information on HEAD. Just FYI, the version number on HEAD already include 5.10.x.
So we'll need to patch OpenACS 5.9 to work with PostgreSQL 8.4, because we need to test with quite a lot of existing installations.
The recommended action is certainly to upgrade pg8.4 to 9.*. this is typically just a pg-dump + pg-restore (since pg 9.0, there is pg_upgrade). Pg documentation  contains an example for using pg_upgrade from 8.4.