Chapter 14. Concurrency Control
For the most part, today's DBMSs are intended as shared resources. 1 A single database may be supporting thousands of users at one time. We call this type of use concurrent use. However, although many users are working with the same database, it does not mean that more than one user is (or should be) working with exactly the same data as another at precisely the same moment.
1As mentioned earlier in this book, a major exception to this statement is Microsoft Access, which is designed for a single user at a time.
It is physically impossible for two users to read or write exactly the same bit on a disk at precisely the same time. Operating systems and hardware disk controllers work together to ensure that only one ...

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