Concurrency Considerations

Database resource control requires the use of data modification rules. There are concurrency anomalies that we will consider when referring to the previous scenario. They include:

  • Lost update

  • Uncommitted read

  • Nonrepeatable read

  • Phantom read

Lost Update Problem

A lost update problem occurs when the same data is changed multiple times when it shouldn't be. The last successful change to the data is kept, and the first change is overwritten. In the previous scenario, PM1 has Jason in his office, discussing project MA2100. He brings up the screen with the project assignments ready to make the update. Meanwhile, PM2 is also discussing the same project with Michael and assigns the project to Michael. PM1's discussion took longer, ...

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