11. Ken Birman developed the virtual synchrony model in a series of papers published between 1985 and 1987. 12. Partly this relates to ordering : virtual synchrony often weakens the message delivery ordering to gain performance. 13. Virtual synchrony was first supported by the Cornell University and was called the " Isis Toolkit ".14. Yet virtual synchrony lets the user treat failure notifications ( view changes ) as trustworthy, infallible events. 15. Virtual synchrony is useful for more than just replicating data, although replication is probably the most common use.16. In virtual synchrony systems, the application programmer signals to the platform what form of ordering is really needed. 17. Virtual synchrony is usually presented to programmers through a simple distributed programming library that supports at least three basic interfaces.18. Experience with virtual synchrony shows that for most applications, the weak but fast form of delivery is just fine. 19. Using the virtual synchrony model, it is relatively easy to maintain fault-tolerant replicated data in a consistent state. 20. But the other sense in which virtual synchrony is a weaker model relates to exactly what happens when some process crashes.
