Forum OpenACS Q&A: Re: Remote Postgresql DB Server
Not only is it possible, but in some cases I would strongly recommend it.
I use this strategy (db on one machine, many OpenACS instances on another) for all my shared OpenACS hosting accounts.
The main advantage is that the CPU utilization is spread across 2 machines rather than one. As well, the filesystem's buffer cache on the db machine is thus dedicated to Postgres I/O - there are no other processes competing for use of the disk.