Idit Keidar and
Esti Yeger Lotem.
Technical Report CS96-7, Institute of Computer Science,
The Hebrew University of Jerusalem, Jerusalem, Israel, June 1996.
Distributed applications often use quorums in order to guarantee
consistency. With emerging world-wide communication technology, many
new applications (e.g. conferencing applications and interactive
games) wish to allow users to freely join and leave, without
restarting the entire system. The dynamic voting paradigm allows such
systems to define quorums adaptively, accounting for the changes in
the set of participants. Furthermore, dynamic voting was proven to be
the most available paradigm for maintaining quorums in unreliable
networks. However, the subtleties of implementing dynamic voting were
not well understood, in fact many of the suggested protocols may lead
to inconsistencies in case of failures. Other protocols severely limit
the availability in case failures occur during the protocol. In this
paper we present a robust and efficient dynamic voting protocol for
unreliable asynchronous networks. The protocol consistently maintains
the primary component in a distributed system. Our protocol allows the
system to make progress in cases of repetitive failures in which
previously suggested protocols block. The protocol is simple to
implement, and its communication requirements are small.
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