Abstract: A method, apparatus, system, and signal-bearing medium that in an embodiment determine, after a restore of a version of an object, where to begin applying changes from a change log to the object based on an identification in the saved version of the object. When a save command for an object is received, an identification of the change log entry associated with the save command is stored in the saved version of the object. Changes to the object then continue to be logged to the change log. After the saved version of the object is restored, the identification in the saved version of the object is used to find the change log entry at which to start applying changes from the change log to the object. In this way, the point in the change log at which to start applying changes to the object may be determined based on the saved version of the object. In an embodiment, this allows the object to continue to be accessed while the save operation is performed.

Abstract: An index recovery mechanism recovers all indexes that were journaled and may be fully recovered during IPL. In addition, the index recovery mechanism performs a first stage of processing for any index that was journaled but cannot be fully recovered during IPL. The first stage processing includes storing index recovery data for an index during IPL. Once IPL is complete, the index recovery mechanism performs a second stage of processing by reading the index recovery data that was stored during IPL, and completing recovery of the index. By performing this two-stage index recovery, the first stage during IPL and the second stage post-IPL, indexes that cannot be fully recovered during IPL can still be journaled and recovered.

Abstract: A flux indicator is utilized as a low-overhead consistency check for a shared resource such as a data structure, and provides a mechanism for determining both whether a data structure has or is currently in the process of being modified. In connection with attempts to modify the data structure, the flux indicator is updated from a first state to a second state prior to modifying the data structure, and thereafter updated to a third state after modifying the data structure, Copies of the flux indicator are then obtained both before and after attempting to obtain a copy of data from the data structure. The validity of the copy of the data is ensured when the first copy of the flux indicator does not indicate that the data structure is in the progress of being modified and the first and second copies of the flux indicator have the same state.

Abstract: A database manager selectively caches journal entries for certain database changes based on dynamic selection criteria. Preferably, a journal disk drive is provided for storing changes to the database. Database change entries are sequentially cached in a main memory journal buffer, awaiting journal write. When a buffer is filled, its buffer contents are written to the journal disk. However, certain change operations will cause the contents of the buffer to be written to the journal disk immediately, before filling the buffer. Certain database change entries selectively cause the buffer to be written, depending on dynamic selection criteria. Preferably, these selection criteria take into account both the estimated time to recover in the event of a system crash and the current level of activity on the system. Generally, the busier the system, the more data will be cached, and vice versa.

Abstract: Disclosed is an enhanced database journaling mechanism that results in reduced secondary storage consumption. The memory management mechanism of the present invention reduces journal size, and accordingly, secondary storage utilization by monitoring the effects to the journal by certain transactions and by making one or more adjustments to reduce those effects.

Abstract: A flux indicator is utilized as a low-overhead consistency check for a shared resource such as a data structure, and provides a mechanism for determining both whether a data structure has or is currently in the process of being modified. In connection with attempts to modify the data structure, the flux indicator is updated from a first state to a second state prior to modifying the data structure, and thereafter updated to a third state after modifying the data structure, Copies of the flux indicator are then obtained both before and after attempting to obtain a copy of data from the data structure. The validity of the copy of the data is ensured when the first copy of the flux indicator does not indicate that the data structure is in the progress of being modified and the first and second copies of the flux indicator have the same state.

Abstract: A database manager selectively caches journal entries for certain database changes based on dynamic selection criteria. Preferably, a journal disk drive is provided for storing changes to the database. Database change entries are sequentially cached in a main memory journal buffer, a waiting journal write. When a buffer is filled, its buffer contents are written to the journal disk. However, certain change operations will cause the contents of the buffer to be written to the journal disk immediately, before filling the buffer. Certain database change entries selectively cause the buffer to be written, depending on dynamic selection criteria. Preferably, these selection criteria take into account both the estimated time to recover in the event of a system crash and the current level of activity on the system. Generally, the busier the system, the more data will be cached, and vice versa.

Abstract: Disclosed is an enhanced database journaling mechanism that results in reduced secondary storage consumption. The memory management mechanism of the present invention reduces journal size, and accordingly, secondary storage utilization by monitoring the effects to the journal by certain transactions and by making one or more adjustments to reduce those effects.

Abstract: A method, apparatus and computer program product are provided for verifying integrity of predefined data structures in a computer system. A central software failure map is stored which includes for each of the predefined data structures a corresponding in-flux bit. The corresponding in-flux bit is set in response to a request to update one of the predefined data structures. Then updating of one of the predefined data structures is performed. The corresponding in-flux bit is reset in response to completing the update of the one of the predefined data structures. During recovery, the corresponding in-flux bits are checked to identify any unstable data structures.