System and method for replication of distributed databases that span multiple primary nodes

1. Field of the Invention A method and system for backing up primary nodes onto backup nodes where the primary nodes can each originate a distributed transaction and can participate in a distributed transaction. The backup nodes, after a primary node failure, undo all transactions whose state is unknown on the backup node and all committed transactions which, if kept, would lead to an inconsistent set of backup nodes. First, committed transactions are undone if commits for them were not received on all back up nodes to the primary nodes that participated in the transaction. Second, all committed transactions that potentially depend on the committed transactions that were undone are also undone. Only those transactions that are provably independent of the committed transactions that were undone are kept. The result is a set of back up nodes which can support operations until the failing primary node is restored.