Tandem Computers Incorporated

Compaq Computer Corporation, Inc.

Larry W Emlich

Robert Lennie

Charles Stuart Johnson

Charles W Johnson

Srini Brahmaroutu

Paul Komosinski

John Lonczak

A monitor function is implemented to monitor and control service processes and other system entities that perform tasks on a distributed network. The monitor function tracks the demise and instantiation of processes and entities that either export or import instrumentation. Any service process or other system entity (driver, interrupt handler, system library procedure) can export instruments (indicators, controls, testpoints). Instrument updates are propagated automatically if they are significant. The importing process conveys the information to a management system so that a human operator, or automated system, can observe and control the operation of the network service. One aspect of the invention uses a backup exporter to take over the processing of an exporter that has become nonfunctional. Another aspect of the invention determines when a CPU has gone down and acts accordingly to identify service processes that were associated with an exporter in the down CPU. For each exporter in the down CPU, any importer that was monitoring with the exporter must perform a switchover to monitor instrumentation on the new exporter in a fault tolerant manner. Additional methods are disclosed which implement fault tolerant monitoring and control in a distributed network.

Enhanced instrumentation software in fault tolerant systems

A computer program product simulates shared code threads with Windows NT fibers. Computer code is included for reusing shared code threads which complete.

Simulating shared code thread modules with shared code fibers

A method of checking a large and/or replicated databases includes forming a position sensitive checksum for each entry of the database to be used in the check. The checksums are then exclusive Ored with one another to form a first database checksum. Periodically, the checksums are again created from each of the entries of the check and a second database checksum formed and compared to the first for a match that indicate checked entries of the database have not changed. In another embodiment, a modification to one of the check entries may be provided, accompanied by a master checksum indicative of what the first checksum should be after the entry is modified. The database entry is modified, and a position checksum value for the entry as modified is created. The checksum value for the modified entry, and for the entry before the modification, are exclusive OR with the first checksum value, and that result compared with the master checksum to ensure that the modification was properly made and that the database remains credible.

Method of comparing replicated databases using checksum information

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San Jose, CA, United States of America

Larry W Emlich