fault tolerant patent

So I don’t understand the novelty in the methods here over the Glazer patent.

The replica supervisors provide interfaces to the replicas that are the same as the interface provided by the operating system. Thus, when one of the replicas makes a call to the operating system, the corresponding replica supervisor is invoked and the supervisor ensures that the effect of the intercepted call is the same regardless of whether the primary or backup performs the operation. When the primary supervisor intercepts a call by the primary replica, the primary supervisor makes the call to the operating system on behalf of the replica and then delivers the results of the operating system call (the “values returned by the operating system”) to the primary replica. In other words, the primary supervisor causes a transformation in the state of the primary replica that is equivalent to the transformation the operating system would have caused if the call had not been intercepted.

The primary supervisor also sends a message to the backup replica. The message contains the values returned by the operating system. When the backup supervisor intercepts a call to the operating system by the backup replica, the backup supervisor does not call the operating system on behalf of the backup replica. Instead, the backup supervisor uses the values sent by the primary supervisor, as a result of the corresponding call by the primary replica, to transform the state of the backup replica. Thus, the replica supervisors ensure that the primary and backup replicas undergo equivalent transformations of their application state as a result of corresponding calls to the operating system.


Inventors: Bressoud; Thomas C. (Northborough, MA), Ahern; John E. (Sudbury, MA), Birman; Kenneth P. (Ithaca, NY), Cooper; Robert C. B. (Wellesley, MA), Glade; Bradford B. (Harvard, MA), Schneider; Fred B. (Ithaca, NY), Service; John D. (Chelmsford, MA)
Assignee: Stratus Computer, Inc. (Marlboro, MA)
Appl. No.: 08/565,145
Filed: December 1, 1995

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More specifically, the invention contemplates a parallel computer system having at least a first and a second primary task performing means and a first and a second secondary (backup) task performing means. The task performing means are interconnected by a message bus means. In such a system, there is contemplated the method of sending messages among the task performing means. In particular, the invention contemplates sending messages from the first primary task performing means to the second primary task performing means which operates on the messages in accordance with the task associated with such means. The second primary task performing means operates on the received messages by initially storing a received message in a queue and thereafter reading the message from the queue for processing. In addition, this second primary task performing means accumulates a count of the messages it reads from the queue. At the same time, or immediately thereafter, the primary task performing means sends the same messages to the second secondary task performing means which stores these messages in a message queue associated therewith. The messages stored in the queue of the second secondary task performing means are only processed if there is a failure of the second primary task performing means.

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