A method of generating a backup copy of a database system. Modifications made to the database since the generation of a prior backup copy are summarized in a bit map on a page basis. When the next backup copy is made, only modified pages are transmitted and merged with the prior copy. Plural backup passes are made. New modifications are allowed to occur to the database on all but the last pass. Any database modification made at an address that has already been examined during a pass is backed-up during the next pass. Modifications are locked out at the beginning of the last pass to allow the final generation of a consistent and complete backup copy.
Method and means are provided for simulating a contiguous data space within a computer memory, and for placing and accessing data objects of various sizes within the simulated contiguous data space. Multiple, sub-data spaces are concatenated in such a way that each page and each sub-data space in the contiguous data space are uniquely identified. Data objects are placed in the contiguous data space and at the first reference to a page of the data object, only the segment containing the referenced page in the contiguous data space is mapped to the database storage disk. Once a data space page is mapped, the operating system can read the page into memory without requesting a disk operation from the database manager. On modifying a page, if the database disk page location is changed, the contiguous data space page is remapped without changing the page address in the data space. Also, modified data pages are rewritten to the database storage disk in an ongoing manner set by the user, instead of at intervals set by the operating system.
A method for recording the data state in a data processing system when an exceptional situation determined by prescribed characteristics is reached for a triggering program in the data processing system. For this purpose, at least one relevant data set which is at least indirectly affected by an access operation by the triggering program and is intended for subsequently deducing the circumstances leading to the exceptional situation is selected on the basis of a prescribed rule, and a recording copy of the content of the at least one relevant data set is then created in a form which permits transfer to another data processing system independently of the triggering program.
A data processing system for managing stored data is described. A log recording incremental updates to the data is provided for data recovery purposes in the event of a system failure. A backup copy of at least a portion of the stored data can be made without closing that portion for update. Any in-progress modifications at the time the backup is taken are allowed for by calculating a recovery point before the time of the backup, from which point recovery is to be performed using the recovery log. The recovery point depends at least in part on the start time of the oldest in-progress data file update.
A method and apparatus for performing a bit map search of the allocation state of memory pages in a computing system. A competitive search is accomplished by a pair of dedicated microprocessors, each of which implements a differently optimized search procedure, to find a bit indicating an un-allocated page in the memory. The first processor to find such a bit interrupts the other processor. The first processor then calculates the free page location and informs the computing system of the location. The other processor is responsible for updating the bit map and summary buffers.
A computer data backup method where copying of data blocks from one medium to another is deferred until a data structure, e.g. a bit map, is generated defining those data blocks that in fact contain data. The data structure is then read to copy to the backup medium the data-containing blocks as defined by the data structure. Since the data structure is generated before the copying is effected, a range of contiguous data-containing blocks is determinable such that all the blocks of that contiguous range may be copied as a single continuous operation. The magnitude of required backup storage is reduced by eliminating the copying of empty blocks in general unless the number of empty blocks between two ranges of contiguous data-containing blocks is less than a predefined number.
