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Summary: Zyzzyva: Speculative Byzantine Fault Tolerance
Ramakrishna Kotla, Lorenzo Alvisi, Mike Dahlin, Allen Clement, and Edmund Wong
Dept. of Computer Sciences
University of Texas at Austin
{kotla,lorenzo,dahlin,aclement,elwong}@cs.utexas.edu
ABSTRACT
We present Zyzzyva, a protocol that uses speculation to re-
duce the cost and simplify the design of Byzantine fault
tolerant state machine replication. In Zyzzyva, replicas re-
spond to a client's request without first running an expensive
three-phase commit protocol to reach agreement on the or-
der in which the request must be processed. Instead, they
optimistically adopt the order proposed by the primary and
respond immediately to the client. Replicas can thus be-
come temporarily inconsistent with one another, but clients
detect inconsistencies, help correct replicas converge on a
single total ordering of requests, and only rely on responses
that are consistent with this total order. This approach al-
lows Zyzzyva to reduce replication overheads to near their
theoretical minima.
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