Communication-efficient and crash-quiescent Omega with unknown membership

The failure detector class Omega (Ω) provides an eventual leader election functionality, i.e., eventually all correct processes permanently trust the same correct process. An algorithm is communication-efficient if the number of links that carry messages forever is bounded by n, being n the number of processes in the system. It has been defined that an algorithm is crash-quiescent if it eventually stops sending messages to crashed processes. In this regard, it has been recently shown the impossibility of implementing Ω crash quiescently without a majority of correct processes. We say that the membership is unknown if each process pi only knows its own identity and the number of processes in the system (that is, i and n), but pi does not know the identity of the rest of processes of the system. There is a type of link (denoted by ADD link) in which a bounded (but unknown) number of consecutive messages can be delayed or lost. In this work we present the first implementation (to our knowledge) of Ω in partially synchronous systems with ADD links and with unknown membership. Furthermore, it is the first implementation of Ω that combines two very interesting properties: communication-efficiency and crash-quiescence when the majority of processes are correct. Finally, we also obtain with the same algorithm a failure detector () such that every correct process eventually and permanently outputs the set of all correct processes

“Implementación de un algoritmo para la selección de un nodo líder en redes de sensores inalámbricas”

El estudio y diseño de algoritmos tolerantes a fallos dentro del campo de las aplicaciones distribuidas incluyen múltiples tareas complejas. Uno de los problemas más importantes y que requiere bastante capacidad de análisis es el consenso, el cual hace referencia a distintos procesos procurando alcanzar un acuerdo común. Este tipo de problema no puede ser resuelto fácilmente en un sistema donde existe la posibilidad que los procesos fallen. Los profesores Tushar Deepak Chandra y Sam Toueg con la finalidad de brindar una solución a este tipo de inconveniente plantearon los detectores no fiables de fallos. El presente trabajo investigativo realiza un análisis y un estudio del algoritmo detector no fiable de fallos Omega planteado por los profesores Tushar Deepak Chandra y Sam Toueg, el mismo que incluye un modelo fallo/recuperación (Crash-Recovery), cuya característica principal se centra en mantener la disponibilidad y el correcto funcionamiento de la red cuando un nodo falla sin que esto afecte a todo el sistema. Específicamente el enfoque se centra en el desarrollo de un simulador que permita observar el funcionamiento del algoritmo detector de fallos Omega en sistemas en donde los procesos puedan fallar y posteriormente recuperarse, en dichos casos se ha demostrado que se puede resolver mediante un consenso. Se realiza un estudio del algoritmo detector de fallos Omega aplicando el modelo de fallo y recuperación. Luego de un exhaustivo análisis y estudio del algoritmo, se procede con la implementación del mismo, mediante un simulador desarrollado en lenguaje C#. Como parte final de la investigación se presenta las conclusiones y recomendaciones, en las cuales se expone los resultados obtenidos de toda la investigación, y recomendaciones para futuros estudios o implementaciones de esta tecnología

Agreement in wider environments with weaker assumptions.

The set agreement problem states that from n proposed values at most n?1 can be decided. Traditionally, this problem is solved using a failure detector in asynchronous systems where processes may crash but do not recover, where processes have different identities, and where all processes initially know the membership. In this paper we study the set agreement problem and the weakest failure detector L used to solve it in asynchronous message passing systems where processes may crash and recover, with homonyms (i.e., processes may have equal identities) and without a complete initial knowledge of the membership

Set agreement and the loneliness failure detector in crash-recovery systems

The set agreement problem states that from n proposed values at most n-1 can be decided. Traditionally, this problem is solved using a failure detector in asynchronous systems where processes may crash but not recover, where processes have different identities, and where all processes initially know the membership. In this paper we study the set agreement problem and the weakest failure detector L used to solve it in asynchronous message passing systems where processes may crash and recover, with homonyms (i.e., processes may have equal identities) and without a complete initial knowledge of the membership