A primary concern of a multiuser database management system is how to control concurrency, or the simultaneous access of the same data by many users. Without adequate concurrency controls, data could be updated or changed improperly, compromising data integrity.

If many PEOPLE are accessing the same data, one way of managing data concurrency is to make each user wait his or her turn. The goal of a database management system is to reduce that wait so it is either nonexistent or negligible to each user. All data manipulation language statements should proceed with as LITTLE interference as possible and destructive interactions between concurrent transactions must be prevented. Destructive interaction is any interaction that incorrectly updates data or incorrectly ALTERS underlying data structures. Neither performance nor data integrity can be sacrificed.

Oracle resolves such issues by using various types of locks and a multiversion consistency model. Both FEATURES are discussed later in this section. These features are based on the concept of a transaction. It is the application designer’s RESPONSIBILITY to ensure that transactions fully exploit these concurrency and consistency features.

A primary concern of a multiuser database management system is how to control concurrency, or the simultaneous access of the same data by many users. Without adequate concurrency controls, data could be updated or changed improperly, compromising data integrity.

If many people are accessing the same data, one way of managing data concurrency is to make each user wait his or her turn. The goal of a database management system is to reduce that wait so it is either nonexistent or negligible to each user. All data manipulation language statements should proceed with as little interference as possible and destructive interactions between concurrent transactions must be prevented. Destructive interaction is any interaction that incorrectly updates data or incorrectly alters underlying data structures. Neither performance nor data integrity can be sacrificed.

Oracle resolves such issues by using various types of locks and a multiversion consistency model. Both features are discussed later in this section. These features are based on the concept of a transaction. It is the application designer’s responsibility to ensure that transactions fully exploit these concurrency and consistency features.