By Philip A. Bernstein, Vassos Hadzilacos and Nathan Goodman
For over 20 years, businesses have been moving their data processing activities on-line. Many businesses, such as airlines and banks, are no longer able to function when their on-line computer systems are down. Their on-line databases must be up-to-date and correct at all times.
In part, the requirement for correctness and reliability is the burden of the application programming staff. They write the application programs that perform the business’s basic functions: make a deposit or withdrawal, reserve a seat or purchase a ticket, buy or sell a security, etc. Each of these programs is designed and tested to perform its function correctly. However, even the most carefully implemented application program is vulnerable to certain errors that are beyond its control. These potential errors arise from two sources: concurrency and failures.
Multiprogramming is essential for attaining high performance. Its effect is to allow many programs to interleave their executions. That is, they execute concwrently. When such programs interleave their accesses to the database, they can interfere. Avoiding this interference is called the concurrency control problem.