Stratus Computer, Inc.

John E Ahern

Bradford B Glade

Kenneth P Birman

Fred B Schneider

John D Service

Robert C Cooper

Thomas C Bressoud

Richard K Gostanian

In a fault-tolerant computer system, a primary replica supervisor is interposed between an operating system and a primary replica of an application program being executed by a primary processor. An object-code editor locates calls to the operating system and loops in the application program and inserts instruction sequences that enable the replica supervisor to intercept the calls to the operating system, results returned by the operating system as a result of the calls and asynchronous events delivered by the operating system to the replica. A backup replica supervisor is similarly interposed between an operating system and a backup replica of the application program being executed by a backup processor. The primary replica interacts with an environment. The replica supervisors ensure that the backup replica undergoes state transformations, as a result of the calls to the operating system and asynchronous events, that are equivalent to state transformations that the primary replica undergoes as a result of corresponding calls and asynchronous events. Thus, after a failure in the primary processor, the backup replica can interact with the environment in a manner consistent with interactions between the primary replica and the environment prior to the failure.

Transparent fault tolerant computer system

An actively replicated, fault-tolerant database system based on a state machine approach that supports the concurrent execution of multiple transactions requested by a plurality of application clients communicating with the system. The system includes a plurality of database servers for storing system data and an application server layered over each database server for controlling the access to and the manipulation of data stored at the underlying database server. The application servers replicate system data to at least one other database server and coordinate the execution of transactions at each database server to ensure consistent data replicas across the system. More specifically, the application servers administer one of two preselected, novel coordination protocols governing the execution of each database-dependent transaction. The protocols assure transaction atomicity and consistent data replication across the entire system as well as continued processing despite database server and communications failures.

Preforming concurrent transactions in a replicated database environment

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Sudbury, MA, United States of America

John E Ahern