Remote duplicate database facility featuring safe master audit trail

Abstract

A local computer system has local database, application programs that modify the local database, an a transaction manager that stores audit records in a local audit trail reflecting those application program modifications to the local database. A remotely located computer system has a backup database. A remote data duplication facility (RDF) is partially located in the local computer system and partially in the remote computer for maintaining virtual synchronization of the backup database with the local database. The RDF includes an extractor process executed by said local computer system, and a receiver process and a plurality of updater processes executed by the remote computer system. The extractor process extracts audit records from a local audit trail and transmits those records to the receiver process. The receiver process distributes the audit records into one or more image trail files that are associated with a particular updater process. Each updater process reads the audit records in its assigned image trail file and initiates redo operations of database modifications denoted in at least a subset of the audit records against the backup database. Each image trail file has a corresponding image trail buffer that is used to accumulate a number of audit records before they are stored in the corresponding image trail file. Before an updater process applies an audit record against the backup database, it requests from the receiver process the status of the transaction associated with the audit record. Status audit records are stored in a transaction status table as well as in a master image trail file. The RDF system herein described provides a method and system for assuring that each audit record is preserved in the system in the event a failure occurs to any of the processes in the RDF.