SYSTEM FOR SELECTIVELY REGISTERING AND BLOCKING REQUESTS INITIATED BY OPTIMISTIC AND PESSIMISTIC TRANSACTIONS RESPECTIVELY FOR SHARED OBJECTS BASED UPON ASSOCIATED LOCKS

A method is disclosed for concurrency control in a system having both pessimistic and optimistic transactions, comprises the steps of entering locks on objects both for optimistic and pessimistic transactions, and validating an optimistic transaction at commit time by checking that all objects on which said optimistic transaction holds a lock have not become obsolete during the execution of said optimistic transaction. Further, a system is shown enabling optimistic and pessimistic transactions to coexist, comprising a lock table into which locks are entered for both optimistic and pessimistic transactions, a wait queue in which pessimistic transactions are entered to wait for locks held by either optimistic or pessimistic transactions, a conflict table which is referenced to determine if a lock held by a first transaction is a conflict lock with respect to a lock requested by a second transaction, and code connected to the lock table, wait queue, and conflict table. This code which is responsive to transaction requests, updates the lock table and the wait queue so that optimistic transactions do not wait for locks to release, whereas pessimistic transactions do wait for locks to release. Other systems and methods are also disclosed.