Oracle International Corporation

Ken Lee

Alok Kumar Srivastava

Sameer Arun Joshi

Surojit Chatterjee

Jonathan Creighton

Techniques are provided for managing replicated data items in a cluster of shared nothing nodes. The techniques include synchronously propagating changes to one or more replicas, while asynchronously propagating changes to the remaining replicas. Because the replicas to which the change is synchronously replicated may be a relatively small percentage of the total number of replicas, the overhead associated with performing an update is reduced. The process of selecting which nodes are involved in the synchronous update operation may take into account a variety of factors, including which replicas are available at the time the update operation is being performed.

Replicating data across the nodes in a cluster environment

Less-restrictive techniques are provided for ensuring that replicated-data systems will never provide out-of-date version of data items. A replicated-data system maintains a version number, a membership group identifier, and a membership count, with each replica of a data item. These values are maintained in such a way as to allow the replicated-data system to reliably satisfy some read requests even though half, or less than half, of the replicas of the data item are available.

Providing the latest version of a data item from an N-replica set

A group of shared-storage resources are being maintained as replicas by the nodes of a cluster. Each node in the cluster maintains a set of pointers to the members of the group. As membership changes, the set of pointers should be changed accordingly. For various, reasons, the set of pointers of a node are not changed and may point to shared-storage resources that are no longer members of the group and/or not point to shared-storage resources that are members of the group. By recording a history of membership changes in the shared-storage resources, and comparing the recording to what a node thinks the shared resources should be, an incorrect set of pointers can be detected and corrective active undertaken.

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San Jose, CA, United States of America

Ken Lee