Clustering, parallelised operating system, super-computing

Hi,
I've been told that PostgreSQL and other similar databases don't work
well on a parallelised operating system because they make good use of
shared memory which does not cross the boundary between nodes in a
cluster.

So I am wondering if any work is being done to make it possible to
have a single database schema that spans a number of hosts?

For example, a table on one host/node that has a reference to a table
on another host/node with deletes cascading back.
e.g.

on host A:

create table person (
username text not null unique primary key,
...
);

on host B:

create table race_entry (
person text
references person(username)
match full
on delete cascade
on update cascade,
...
);

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