A number of on going research projects follow a partition-based approach to provide highly scalable distributed storage services. These systems maintain namespaces that reference objects distributed across multiple locations in the system. Typically, atomic commitment protocols, such as 2-phase commit, are used for updating the namespace, in order to guarantee its consistency even in the presence of failures. Atomic commitment protocols are known to impose a high overhead to failure-free execution. Furthermore, they use conservative recovery procedures and may considerably restrict the concurrency of overlapping operations in the system. This paper proposes a set of new protocols implementing the fundamental operations in a distributed namespace. The protocols impose a minimal overhead to failure-free execution. They are robust against both communication and host failures, and use aggressive recovery procedures to re-execute incomplete operations. The proposed protocols are compared with their 2-phase commit counterparts and are shown to outperform them in all critical performance factors: communication roundtrips, synchronous I/O, operation concurrency.
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