Re: About the current situation of distributed systems.

I am developing a client - server system that could work separately but
if needed, could merge in to one system easily.

For example, we could sell the system to 2 different cities, but when
our customer needed, we could connected the 2 systems as if there is
only one system but more data and resources.

So I am think about use distributed system to solve the problem. When
the system needed to be connected, just build a distributed system and
run only one server program with 2 database instead of one.

I am not sure if the physical distance would be a serious problem if we
use distributed system.
I would approach your problem with a help of grid tools and applications.

You can use metascheduler / grid broker <http://en.wikipedia.org/wiki/Metascheduler> to distributed jobs (application tasks) into 2 clusters (systems).
You will also need some data replication <http://en.wikipedia.org/wiki/Data_replication> tools for moving data from 2 sites to 1 site either periodically or on-demand.

If you have good quality network interconnections between these sites, physical distance will not matter.

Best,
Chris
--
Chris Wilk chris.wilk@xxxxxxxxxxxxxxxx
Senior Consultant

GridwiseTech office/fax: +48 12 294 71 20
.