wish: limit number of connections per database

Dear List,

I already asked my question on the admin list, but got no answer. As I
even could not find any related information anywhere, I think my
question is a wish:

Would it be possible to set the maximum number of connections to each
database individually? I need this because the server will be shared
between several users and I want to avoid that that somebody uses the
maximum number of connections possible to the server, locking out others.

I am not familiar with the internals of postgresql, but maybe a column
in pg_database could store the limit if any.

A similar solution would be if the number of connections could be
limited per users, a similar column in pg_user could store the limit.

Or this limit could be configured as an additional column in pg_hba.conf.

How hard would it be to implement such a feature? As there is a check on
each new connection to the server, maybe it would not be too difficult
to check one constraint more :-)

I don't have much time to do it, but if you think it is not too hard and
my limited knowledge in C is enough I would help doing it gladly.

These feature would be good even as a "hidden" feature, configurable
only through psql after startup (file configuration support added later).

thanks,

attila