6. Transactions

A transaction is an application program consisting of a sequence of SQL instructions (database modification and query). It ends with a commit or a rollback. The DBMS is a multi-user software application that allows the simultaneous execution of several transactions to improve database availability. In addition, it provides each transaction with an execution environment that appears to be isolated from other transactions. The aim of transaction optimization is to detect and resolve undesirable effects that one transaction may produce on other transactions, such as slowing down or preventing validation. Next, we present the mechanisms that control concurrent access to the database and their impact on performance.