Wait depth limited concurrency control

A new class of wait depth limited (WDL) concurrency control (CC) methods is described. The WDL policy is shown by simulations to be effective both in systems with proportionately large I/O latencies as well as in systems with large numbers of processors. WDL is also attractive in terms of implementation. In many applications little or no system modification may be required other than the CC code. Since it is a lock-based method, unlike optimistic methods, there is no need for private copies of modified data for each transaction, nor is there any need for snapshot, timestamp, or versioning mechanisms to guarantee that transactions are always provided with a fully consistent database image