OBJECT HASHING WITH INCREMENTAL CHANGES

摘要

A method and system are provided for reconfiguring a multiple node system after an epoch change in a manner that reduces the overhead and system unavailability typically incurred during reconfiguration. A resource-to-master mapping is established using the combination of a resource-to-bucket hash function and a buket-to-node hash function. The resource-to-bucket hash function is not changed in response to an epoch change. The bucket-to-node hash function does change in response to epoch changes. Techniques are disclosed for adjusting the dynamic bucket-to-node hash function after an epoch change in a manner that load balances among the new number of nodes in the system. Further, the changes to the bucket-to-node assignments are performed in a way that reduces the number of resources that have to be remastered. In one embodiment, only those resources that lose their masters during an epoch change are assigned new masters during an initial reconfiguration. Load balancing is then gradually achieved by migrating resources after the system has been made available. The old masters of resources forward access requests to new masters of resources once they have transferred the master resource objects for the requested resources. In addition, techniques are disclosed for migrating resources from a node in anticipation of a planned shutdown of the node.