Kevin Smathers

Efficient eventual consistency in Pahoehoe, an erasure-coded key-blob archive

Cloud computing demands cheap, always-on, and reliable storage. We describe Pahoehoe, a key-value cloud storage system we designed to store large objects cost-effectively with high availability. Pahoehoe stores objects across multiple data centers and provides eventual consistency so to be available during network partitions. Pahoehoe uses erasure codes to store objects with high reliability at low cost. Its use of erasure codes distinguishes Pahoehoe from other cloud storage systems, and presents a challenge for efficiently providing eventual consistency. We describe Pahoehoes put, get, and convergence protocols—convergence being the decentralized protocol that ensures eventual consistency. We use simulated executions of Pahoehoe to evaluate the efficiency of convergence, in terms of message count and message bytes sent, for failure-free and expected failure scenarios (e.g., partitions and server unavailability). We describe and evaluate optimizations to the naïve convergence protocol that reduce the cost of convergence in all scenarios.

Governing the contract lifecycle: a framework for sequential configuration of loosely-coupled systems

Sequential configuration is a fundamental pattern that occurs when integrating systems that span domains and levels of abstraction. This task requires the integration of heterogeneous autonomous information systems, processes, and applications. We propose an extensible system for correlating sequential configurations across loosely-coupled systems. Our framework defines fundamental abstractions and interfaces that enable the implementation of domain-specific models. We build upon our framework to provide a suite of tools to support applications that manage the configuration lifecycle. Our implemented prototype application integrates the processes, tools, and data involved in the first two stages of the IT outsourced services contract lifecycle.

Enabling outsourced service providers to think globally while acting locally

Enterprises commonly outsource all or part of their IT to vendors as a way to reduce the cost of IT, to accurately estimate what they spend on IT, and to improve its effectiveness. These contracts vary in complexity from the outsourcing of a world-wide IT function to smaller, country-specific, deals.