US Patent 7096227 Database utilities

A system and methods for rapid unloading and reorganization of hierarchical databases. Overflow and a window of blocks are progressively read into memory. Unloading proceeds as the scan cylinders window moves ahead. The reading of blocks stays about scan cylinders ahead of the unload. As a segment is unloaded, its space is converted to free IMS space and when appropriate, combined with adjacent free space already in the block. Thus about a window behind the unload point in the database, all of the segments in a block will have been converted to free space making the block one unit of free space.