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??? This goal is the core issue of data
integrity, which, in turn, is the foundation of any database system.
When multiple users access the same data, there is always the possibility that one
user??™s changes to a specific piece of data will be unwittingly overwritten by another
user??™s changes. If this situation occurs, the accuracy of the information in the database
is compromised, which can render the data useless or, even worse, misleading.
At the same time, the techniques used to prevent this type of loss can dramatically
reduce the performance of an application system, as users wait for other users to
complete their work before continuing. These techniques act like a traffic signal, so
youcan??™t solve this type of performance problem by increasing the resources available
to the database. The problem isn??™t due to a lack of horsepower??”it??™s caused by a
red light.
Although concurrency issues are central to the success of applications, they are some
of the most difficult problems to predict because they can stem from such complex
interactive situations.


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