INTRODUCTION Recently a new theory of dlsmbuted computing has been proposed, accordmg to which a dlsmbuted computation 1s vIewed as an activity of knowledge acqulsmon and chssemmatlon by commumcatmg processes (Halpem and Moses [ 19861, Halpem and Fagm [1985]) In addmon to supplymg a formal log& foundation for &smbuted computmg which directly supports the informal way m which dlsmbuted algonthms are often described and thought about, this "knowledge theory" has afforded relatively simple proofs

more »

... f interesting results for specific problems (e g Chandy and msra [1986], Dwork and Moses [1986], Moses and Tuttle [1986]) In this paper, we use the knowledge formahsm to analyse atormc comrmtment protocols employed by transactions m chsmbuted database systems, such as two-phase comnut We charactense the two-phase comnut and three-phase conumt famlhes of protocols in terms of the level of knowledge that must be acquved by a site to commit a tramactlon We show that m the two-phase comnut protocol the declslon to comnnt is reached with the nunlmum knowledge necessary under any atomic comnntment protocol, and that m the three-phase commit protocol the decision to comnut is reached with the mmlmum knowledge necessary under any non-blocking atomic comnutment protocol Our analysis also provides a proof of the fact that there 1s no non-blockmg atonuc comnutment protocol that can tolerate commumcatlon filures (a result anticipated m the work of Gray -cf hn "Generals' Parddox" [1978] and formally proved by Skeen [ 19821 for a model of computation less general than the one used here) Fmally, usmg knowledge theory, we denve a lower bound for the number of messages needed to comrmt a transachon (a previously known result, due to Dwork and Skeen [1983] ) This lower bound 1s