This paper presents two families of nonlocking concurrency control methods for database systems, which are "optimistic" in that they rely mainly on transaction backup rather than locking to prevent conflicts between transactions. These methods are particularly efficient for applications where conflicts between transactions are rare. The paper discusses the limitations of traditional locking approaches, such as overhead, deadlock, and reduced concurrency when large parts of the database are stored in secondary memory. The optimistic approach avoids these issues by allowing transactions to read data without restrictions and only writing to local copies of data, which are then validated and made global if no conflicts are detected. If conflicts are found during validation, the transaction is rolled back and retried. The paper also describes the validation process, which ensures that transactions are serially equivalent, and presents two types of concurrency controls: one with serial validation and another with parallel validation. The optimistic approach is shown to be effective for query-dominant systems and large tree-structured indexes, where it can significantly reduce concurrency control overhead and improve performance. The paper concludes that optimistic methods may be superior to locking methods in systems where transaction conflicts are unlikely.This paper presents two families of nonlocking concurrency control methods for database systems, which are "optimistic" in that they rely mainly on transaction backup rather than locking to prevent conflicts between transactions. These methods are particularly efficient for applications where conflicts between transactions are rare. The paper discusses the limitations of traditional locking approaches, such as overhead, deadlock, and reduced concurrency when large parts of the database are stored in secondary memory. The optimistic approach avoids these issues by allowing transactions to read data without restrictions and only writing to local copies of data, which are then validated and made global if no conflicts are detected. If conflicts are found during validation, the transaction is rolled back and retried. The paper also describes the validation process, which ensures that transactions are serially equivalent, and presents two types of concurrency controls: one with serial validation and another with parallel validation. The optimistic approach is shown to be effective for query-dominant systems and large tree-structured indexes, where it can significantly reduce concurrency control overhead and improve performance. The paper concludes that optimistic methods may be superior to locking methods in systems where transaction conflicts are unlikely.