A fully integrated ability to query across multiple databases,possibly on multiple servers, something Oracle has had for nearly two decades.
That isn't the approach to take. The fact that Oracle has it is not a guarantee that it is useful or good. If you need to query across databases (assuming within the same cluster) then you designed your database wrong and should have used our SCHEMA support (what Oracle calls Namespaces) instead.
This is the difference between developers and real world users. Real world users may not have the ability, time or resources to redesign their databases just because that's the 'best' way to do something. Will it be the most efficient way to do it? Almost certainly not.
I've been involved in a few corporate mergers, and there was a short term need to do queries on the combined databases while the tiger team handling the IT restructuring figured out how (or whether) to merge the dabases together. (One of these happened to be an Oracle/Oracle situation, it was a piece of cake even though the two data centers were 750 miles apart and the table structures had almost nothing in common. Another was a two week headache, the third was even worse!)
In a perfect world, it would be nice if one could do combined queries linking a PostgreSQL database with an Oracle one, or a MySQL one, too. Because sometimes, that's what you gotta do. Even something that is several hundred times slower is going to be faster than merging the databases together. When I do this today, I have to write a program (in perl or php) that accesses both databases and merges it by hand.
Can't you do that with FDW that is present in 9.1?
