Group Membership in Asynchronous Distributed Environments Using Logically Ordered Views
Technical rept. 1 Oct 1991-30 Sep 1992
NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF ELECTRICAL AND COMPUTER ENGINEERING
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A group membership protocol ensures agreement and consistent commit actions among group members to maintain a sequence of identical group views in spite of continuous changes, either voluntary or otherwise, in processors membership status. In asynchronous distributed environments, such consistency among group views must be guaranteed using messages over a network which does not bound message delivery times. Assuming a network that provides a reliable, FIFO channel between any pair of processors, one approach to designing such a protocol is to centralize the responsibility to detect changes, ensure agreement, and commit them consistently in a single manager process. This approach is complicated by the fact that a protocol to elect a new manager with a consistent membership proposal must be executed when the manager itself fails. In this report, we present a membership protocol based on ordering of group members in a logical ring that eliminates the need for such centralized responsibility. Agreement and commit actions are token-based and the protocol ensures that no tokens are lost or duplicated due to changes in membership. The cost of committing a change is 2n point-to-point messages over FIFO channels where n is the group size. The protocol correctness has been proven formally.
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