Improvements in Database Concurrency Control with Locking

Various techniques have been proposed to ensure the safe, concurrent execution of a set of databasetransactions. Locking protocols are the most prominent and widely used of these techniques, with two-phaselocking and tree-locking being but two examples of these protocols. A locking protocol defines ageneral set of restrictions on the placement of lock and unlock steps within transactions. In this paper weshow that it is possible to further increase the potential level of concurrency of a set of transactions,within the context of a specific locking protocol, by further restricting the placement of lock and unlocksteps within each transaction. We also discuss a variation of the tree-locking protocol that allowstransaction to be locked with respect to a dynamically changing set of tree structures. In addition wedefine and discuss the concept of a concurrency cost function for a locked transaction. This cost functionmeasures the potential for conflict of a transaction with other transactions.