> The only assumption I am aware of
> that I am making is that two identical databases, given the same set of
> arbitrary transactions will end up being the same.
Unfortunately I do not think you can make that assumption. Since
response time of the two machines will be different you might end up
generating different data on different servers.
> If an insert/update/delete/DDL command comes, it forwards it to both
> machines.
> If a query comes down the line it forwards it to one machine or the
> other.
Also in PostgreSQL you cannot easily distinguish between read-only
and read-write statements. Not without looking at the query plan.
Thus imho generic replication cannot be achieved by plugging something between
clients and the backend.
Andreas