| 摘要 |
The system, method, and program product of this invention allows a database management system to internally use direct and indirect pointing to locate targeted data elements that are logically related to another data element or are a target of a secondary index. By using direct and indirect pointing, the number of steps involved in a reorganization of the database can be reduced. After a reorganization, the database management system does not go back, in a separate process, to update all of the direct pointers that have pointed to segments that have moved as a result of the reorganization. Instead, the direct pointer is updated, by using the indirect pointer, only upon a first reference to the targeted data element that has moved. Each targeted data element has an entry in an indirect index where a unique identifier of the targeted data element is the key into the index. The indirect index has two direct pointer slots. Which pointer slot is used by the DBMS is determined by the odd/even reorganization number. For each reorganization, the DBMS alternates between the two portions of the indirect index to update the appropriate one of the two pointers with a new location whenever the targeted data element is moved. As a result, the indirect index contains the most recent update and the most recent previous update. If the reorganization fails, the most recent previous pointer is used to find the location of the targeted data element. Consequently, as the reorganization process is proceeding, the update to the assigned slot for the new reorganization number can be made without logging and without involving unnecessary overhead associated with maintaining direct recoverability of the keyed data records.
|
