I've been playing with this sort of thing for a while.

1. Identify missing primary keys and unique constraints
2. Identify the number of fields in the key
3. Identify naming conventions for primary key fields and the equivalent in other tables

[Identify candidate FK where a table contains the equivalent fields as those participating in aa PK[/li]

4. Discount those where there is already an FK relationship
5. Test the data to precheck violations
6. Generate PK & FK scripts through automated means

Text parsing SYS.comments for joins in views should also help Identify candidates but is significantly more involved.

I Have a working box of bits for Vertica,, Teradata, MySql, SQL server and I'm looking to experiment with RedShift in the near future. I think working out how to do this for Postgres would be handy.