I am experimenting with an approach to solving this problem that allows users to log in and create content using web and slave database servers that are geographically close to them while maintaining a single consistent Drupal site. It does not require multiple active database master servers and all the intractable problems that causes. My system, called Pipe Dream, intercepts database-changing operations at the remote locations and sends them over a message queue (a.k.a. a pipe) to the primary location where they are replayed.
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