> Is it possible to stop a single database, like it is with Oracle? Our
> oracle admin asked this for FS backups, if there are 3 dbs (in
> separate tablespaces) then there seems no reason why this couldn't be
> possible... is it possible?
No, this is not possible, because they are all serverd by the same
server process.
You can, however, do an online backup while the database is running.
This is essentially a filesystem backup, and you issue a certain
SQL statement before and after the backup.
> ps. If this isn't possible, what experiences do people have with
> running several postgres instances on a single machine?
It is called 'cluster', not 'instance'.
I have very good experiences.
Yours,
Laurenz Albe