To truly understand how all the disparate pieces of the Oracle database work together, in this section we’ll walk through an example of the steps taken by the Oracle database to respond to a user request. For this example, we’ll look at a user who is adding new information to the database (in other words, executing a transaction).
A transaction, in this case, is a work request from a client to insert, update, or delete data. The statements that change data are a subset of the SQL language called Data Manipulation Language (DML). Transactions must be handled in a way that guarantees their integrity. Although Chapter 7 delves into transactions more deeply, we must visit a few basic concepts relating to transactions now in order to understand the example in this section:
In database terms, a transaction is a logical unit of work composed of one or more data changes. A transaction may consist of multiple INSERT, UPDATE, and/or DELETE statements affecting data in multiple tables. The entire set of changes must succeed or fail as a complete unit of work. A transaction starts with the first DML statement and ends with either a commit or a rollback.
Once a user enters the data for his transaction, he can either commit the transaction to make the changes permanent or roll back the transaction to undo the changes.
A key factor in preserving database integrity is an ...