We have a setup where several databases share a schema with 5 tables.
Many other tables are dependend with foreign keys on these 4 tables,
but each database has its own unique set of these and the data in
those is unique per database: The other schema's and tables between
the slaves are therefore different from each other.
Updates to the shared tables are infrequent (once a day a few records)
and I can enforce that ids (pkeys) will not change or get deleted and
all records are timestamped upon creation.
Each database has its own maintainer(s) and is owned by a different
organisation and each organisation has a few hundred users .

To keep the 4 tables consistent between all the databases, I am
considering slony to replicate the tables from a single source to the
slaves. (Slaves are not allowed to change those tables only the master
may).

Now the catch:
How do I backup the clients? Each night we do a pg_dump on all the
databases. And in case of trouble we need to be able to separately
restore a single database, sometimes even to a version from a few
weeks ago.

How do I get the shared tables in sync with the master, considering
that emptying those tables for a rebuild is not a workable option
because of the foreign key constraints?

Is slony the way to go? or is dbmirror a better solution in this case,
because that doesn't demand to start from an empty table, it just
needs a table that is the same, which although a pain, can be done
manually after the dump is restored and before bringing replication
online again. I'm not even sure if dbmirror is stable enough, it does
not seem to be used a lot.

A third alternative is creating a trigger that contacts all databases
through dblink directly, or just copy/past all the sql statements on
the master via a script to all clients. When I log that with a
timestamp in a file, I can recreate databases up to any point in time
and reissue that sql to the shared tables to make them consistent
again. But that sounds a lot like a manual replication system and I'd
rather use something that is automated.

Any answers, thoughts and comments are welcome!

Floris