Why old DB optimizers cannot deal with the cloud

First article about query optimizers: http://www.databasecolumn.com/2008/06/designing-systems-for-the-grid.html. I hope the following articles will give us much more information! That optimization problem is really interesting. We know it is a NP-complete king of problem. And it is even more interesting when dealing with multiple data sources. That's one of the challenges of a modern Data Services Platform.