Combining Load Balancing with Shared Storage and Primary Backup Replicaton

Abstract

Replication is used to improve availability, reliability and performance. The latter may be improved by routing the requests to the least loaded replicas (load balancing). As a request may be processed by any of the replicas it is possible that the client will observe state older then expected - sometimes. The problem of migrating clients is addressed by session guarantees (sg) which ensure that client will always observe state that is consistent with its own actions. Unfortunately, current sg algorithms concentrate on consistency observed by a client without any performance considerations.