Avaliação de esquemas de contabilidade autônoma em grades computacionais peer-to-peer.

Abstract

Peer-to-peer computational grids have evolved considerably in late years because they allow the sharing of computational resource among organizations. It is important that these systems provide incentives for peers to offer their idle resources. If they do not do so, peers may not want collaborate and the system may collapse. [1] presents the Network of Favors, a decentralized approach based on reputation to solve this problem in the peer-to-peer computational grid OurGrid. However, in order for the Network of Favors to be robust, it is necessary to provide an accounting scheme that is accurate, simple, decentralized and resistant to attacks. Providing an accurate mechanism of accounting for a system in which the parties can have a malicious behavior is not trivial. In this work, we propose the accounting scheme based on relative power of peers, a scheme that accounts the use of resources in a totally autonomous way, that is, only based on information that a local peer can compute. The autonomy of the accounting makes the existence of trust relationships among peers unnecessary. The relative power of a remote peer is an estimate of how fast it is in relation to another. The use of resources by another peer is calculated as a product of the relative power of this peer versus the time in which the resource is available. In order to validate our solution we developed an event-based simulator for peer- to-peer computational grids. With the aid of this simulator, we evaluated the accounting scheme by relative power and compared it with the perfect accounting scheme, an accounting schema fed by perfect information about the computational cost of the application tasks and the computational power of resources - which is not possible to implement in practice for our target systems – and an accounting schema by time, an autonomous accounting schema in which a consumer and a provider of resources measure only the time of the availability of the resource. Our results show that the accounting by relative power is more accurate than the accounting by time for the metrics favor ratio and application response time. In addition to this, the accuracy of the accounting by relative power is very near to the one of the perfect accounting schema.