摘要:
A primary computer system has a database, application programs that modify the local database, and a transaction manager that stores audit records in a local audit trail reflecting those application program modifications to the local database. A plurality of parallel backup systems are used to provide "triple contingency protection" of the data on the primary computer system. However, if the primary system suffers a sudden catastrophic failure, the parallel backup systems will generally be left in inconsistent states. To restart the application programs on one of the backup system, the parallel backup are first synchronized with each other, and then transaction processing is restarted with one of the backup systems as the new primary system, and the other backup systems as the backups to the new primary system. In addition, in order to enable any single backup system's database to be brought into a self consistent state, backup volume Updaters are stopped after database updates for all transactions committed on the primary system before a specified time have been completely applied to the backup system's database. After any reports requiring a self consistent database have been generated, operation of the Updaters is resumed.
摘要:
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.
摘要:
An improved recovery method utilizes sequence numbers to order log records and reduce the excess compensating actions due to a failure during recovery. Next undo records are written to the log after a preset number of compensating actions which include the sequence number of the record currently being scanned. After a failure, all records between the next undo record and the record having the sequence number included in the next undo record are ignored during when the log is scanned backwards.
摘要:
A primary computer system has a database, application programs that modify the local database, and a transaction manager that stores audit records in a local audit trail reflecting those application program modifications to the local database. A plurality of parallel backup systems are used to provide "triple contingency protection" of the data on the primary computer system. However, if the primary system suffers a sudden catastrophic failure, the parallel backup systems will generally be left in inconsistent states. To restart the application programs on one of the backup system, the parallel backup are first synchronized with each other, and then transaction processing is restarted with one of the backup systems as the new primary system, and the other backup systems as the backups to the new primary system. In addition, in order to enable any single backup system's database to be brought into a self consistent state, backup volume Updaters are stopped after database updates for all transactions committed on the primary system before a specified time have been completely applied to the backup system's database. After any reports requiring a self consistent database have been generated, operation of the Updaters is resumed.
摘要:
A method and system for backing up primary nodes onto backup nodes where the primary nodes can each originate a distributed transaction and can participate in a distributed transaction. The backup nodes, after a primary node failure, undo all transactions whose state is unknown on the backup node and all committed transactions which, if kept, would lead to an inconsistent set of backup nodes. First, committed transactions are undone if commits for them were not received on all back up nodes to the primary nodes that participated in the transaction. Second, all committed transactions that potentially depend on the committed transactions that were undone are also undone. Only those transactions that are provably independent of the committed transactions that were undone are kept. The result is a set of back up nodes which can support operations until the failing primary node is restored.
摘要:
A method and system for high-speed database replication. Audit update records and audit backout records are generated by the primary system, and are transmitted to the backup system in multiple streams in parallel. The backup system stores the received audit records as audit image trails, and applies the audit updates and audit backouts to the backup database without regard to whether the transactions committed or aborted and without regard to whether the backup system received a complete set of the audit records pertaining to the transactions. Upon the occurrence of a predetermined event, the backup system applies all the audit updates and backouts it received, and subsequently “undoes” questionable audit updates and audit backouts.
摘要:
A primary computer system has a database, application programs that modify the local database, and a transaction manager that stores audit records in a local image trail reflecting those application program modifications to the local database. In a remote backup system, a Receiver process receives audit records from the primary system. The audit records include audit update and audit backout records indicating database updates and database backouts generated by transactions executing on the primary system. The Receiver stores the audit update and audit backout records in one or more image trails. For each image trail there is an Updater process that applies to a backup database volume the database updates and backouts indicated by the audit update and audit backout records in the image trail. The remote backup system periodically executes a file purge procedure, which identifies the oldest transaction table from among the transaction tables in the last image trail file accessed for each of the image trails. Then, for each image trail, the file purge procedure accesses the image trial files in a predefined chronological order and for each accessed image trail file it compares a first set of newest transaction identifiers in the file's transaction table with a second set of oldest transaction identifiers in the identified oldest transaction table. The procedure purges the accessed image trail file only when all of the transaction identifiers in the first set are older than corresponding transaction identifiers in the second set.
摘要:
A local computer system has a local database, application programs that modify the local database, and a transaction manager that stores audit records in a local audit trail reflecting those application program modifications to the local database. Each audit record has an associated audit trail position. 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 the local audit trail and transmits those records to the receiver process. When the receiver process detects that it is receiving audit records not in accordance with a predefined sequence, it transmits an error message to the extractor process. Otherwise it distributes the received audit records to a plurality of image trail files in the remote computer system for processing by updater processes, which initiate redo operations of database modifications denoted in at least a subset of the audit records against the backup database. The extractor process responds to each error message by obtaining a restart audit trail position value from the receiver process and then extracting audit records from the local audit trail starting at that restart audit trail position value.
摘要:
A method and system for purging database update image files after completion of associated transactions for a database replication system with multiple audit logs. Audit update records and audit backout records are generated by the primary system, and are transmitted to the backup system in multiple streams in parallel. The backup system stores the received audit records as audit image trails, and applies the audit updates and audit backouts to the backup database without regard to whether the associated transactions committed or aborted. Because audit updates and audit backouts are applied without regard to whether the associated transactions committed or aborted, image files containing audit records associated with transactions that have not yet committed or aborted must not be purged. The present invention provides for a method for determining whether an image trail file contains audit records that can be purged such that image trail files can be safely deleted.
摘要:
A primary computer system has a database, application programs that modify the local database, and a transaction manager that stores audit records in a local image trail reflecting those application program modifications to the local database. In a remote backup system, a Receiver process receives audit records from the primary system. The audit records include audit update and audit backout records indicating database updates and database backouts generated by transactions executing on the primary system. The Receiver stores the audit update and audit backout records in one or more image trails. For each image trail there is an Updater process that applies to a backup database volume the database updates and backouts indicated by the audit update and audit backout records in the image trail. The audit update and audit backout records are applied to the backup database volume in same order that they are stored in the image trail, without regard to whether corresponding transactions in the primary system committed or aborted. Upon the occurrence of a predefined event, such as failure of the primary system, the backup system determines a set of primary system transactions for which a commit/abort outcome is unknown. For each image trail, the corresponding Updater completes applying database updates and backouts to the backup database volume. Then, the Updater backs out database updates for the transactions for which the commit/abort outcome has been determined to be unknown.