Private locking and distributed cache management

For a data sharing database system, substantial costs are incurred for global locking, to support both transactions and cache management. Replacing global locks with local locks managed by local lock managers offers the opportunity to substantially reduce locking overhead. To do this requires the exploitation of global covering locks. We discuss covering in general, and describe the conflicts required for both covering and intention locks. We then describe how to generate new covering and intention modes when logical and physical resources are equated in a data sharing system, hence reducing locking overhead. The new intention modes, because they conflict, permit cache management without losing fine grained concurrency. Fine grained concurrency with combined resources was not previously possible