Importance

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Abstract

A method and system for forming a new cluster of servers having state data that is consistent with the state data of a cluster that previously existed. The previous cluster preserves its state data by recording transactions to a log file in conjunction with a sequence number maintained by each node. The node that recorded the transaction then increments its copy of the sequence number and attempts to replicate the transaction to other nodes of the cluster. If the transaction is replicated, each other node commits the transaction and increments its sequence number. If the node fails before it can replicate the transaction, then no other nodes will increment their sequence numbers, whereby the next logged transaction has the same sequence number as the previously logged, but orphaned replicated transaction. When a new node forms a cluster, it unrolls the log file so as to become consistent with the state of the previous cluster. Logged transactions having duplicate sequence numbers indicate that the first such transaction was not fully replicated. To remain consistent, the first transaction is discarded and not used to update the state of the new cluster.

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First Claim