Hi, I am working on a long-range interaction problem, so that communication is "each-to-each", _although very sparse_. My current approach is as follow: 1. If a process owns an object A, it opens a shared window to this object. 2. If another process happens to generate data which belongs to A, which is determined on the fly, it 'put' its share to A. The algorithm works for small number of objects, but I need millions of them. I wonder: 1. Is it possible to increase the number of communicators above 2048? 2. Is it a scalable approach? Again, although that communication is 'each-to-each', it is extremely sparse. Any advise and comments are highly appreciated. Thanks in advance, --Ted