- Induced Determination of Consistent Snapshots

A classical way to determine consistent snapshots consists in using Chandy-Lamport's algorithm. This algorithm relies on speciic control messages that allow processes to synchronize local checkpoint determination and message recording in order the resulting snapshot be consistent. This paper investigates a communication-induced approach to determine consistent snapshots. In such an approach, control information is carried by application messages. Two abstract necessary and suucient conditions are stated: one associated with global checkpoint consistency, the other associated with message recording. A general protocol is derived from these abstract conditions. Actually, this general protocol can be instantiated in distinct ways, giving rise to a family of communication-induced snapshot protocols. This general protocol shows there is an intrinsic tradeoo between the number of forced checkpoints and the number of recorded messages. Finally, a particular instantiation of the general protocol is provided. D etermination d' etats globaux coh erents sans synchronisation explicite R esum e : Le protocole de Chandy et Lamport est le moyen classique de d etermination d' etats globaux coh erents. Il est fond e sur l'emploi de messages de contr^ ole qui permettent de synchroniser les dii erents processus aan d'assurer la coh erence de l' etat global d etermin e. Cet article explore une nouvelle approche qui consiste a faire jouer le r^ ole de messages de synchronisation aux messages de l'application en leur faisant transporter une information de contr^ ole. Pour ce faire, deux conditions n ecessaires et suusantes sont pr e-sent ees. Elle concernent respectivement la coh erence des etats globaux et la journalisation des messages en transit. Le protocole d eriv e de ces deux conditions peut ^ etre instanci e de dii erentes faa cons donnant lieu a une famille de protocoles.