Importance

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Abstract

According to a first aspect of the invention, a DASUM (Durable Atomic Storage Update Manager) provides an extensible framework assuring complex changes to persistent storage of data within a computer system, including a distributed computer system. During normal runtime, modifications to permanent storage are broken down and organized as a plurality of simpler transactions. These simpler transactions are accomplished atomically by executing associated agents within the computer program under execution. Each agent need only have the ability to complete its own process, and need not be able to deal with side effects from other transactions. Without needing to know what steps may be required, each agent supplies three agent-specific procedures that can be called during recovery from a fault. The DASUM provides seven services that, during normal transaction execution, can store information in a logger necessary for recovery from a fault. The recovery information stored in the logger can be used to replicate a dynamic tree-like fault tolerant update set that is maintained by the DASUM on an atomic basis. According to a second aspect of the invention, the DASUM provides recovery from the effects of incompletely executed transactions in the event of a fault. During fault recovery, the DASUM calls the agent specific procedures, as needed, using the recovery and recovery sequence information stored during normal transaction execution. The present invention advantageously permits separating the agents from the logger, simplifies logger design, and improves durability of the data to be persistently stored.

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First Claim