When several sites are accessing the same physical MySql server, the distant sites may experience performances issues.
To resolve that, database server software can be configured to have several database servers synchronized together so that each site uses his own local server but also benefits real-time from the other connected database servers.
If you're using MySQL 5.1+ it's natively supported
If you're using MySQL 5.0- you still have a possibility to configure it manually:
- A simple Master-slave architecture
- A bidirectional/circular replication architecture: there are a couple of nice articles describing the setup process:Advanced MySql Replication or Bidirectional MySql synchronization
- MySql Cluster NDB
Some independant tools exist as well:
Oracle and SQLServer have similar features.