This chapter covers issues relating to concurrency and restore, as well as how to commit or roll back transactions.
In multi-user environment, controlling access and update is essential to protect database integrity and ensure that a user’s transaction will have accurate and consistent data. Without appropriate control, data could be updated incorrectly in the wrong order.
To control parallel operations on the same data, data must be locked during transaction, and unacceptable access to the data by another transaction must be blocked until the end of the transaction. In addition, any updates to a certain class must not be seen by other users before they are committed. If updates are not committed, all queries entered after the last commit or rollback of the update can be invalidated.
All examples introduced here were executed by csql. Outputs in the examples are displayed in italics.