Mumbai University > Information Technology > Sem 3 > Database Management System

Marks: 4M

Year: May 2014, May 2016

Transaction

• A transaction is a set of changes that must all be made together.
• It is a program unit whose execution mayor may not change the contents of a database.
• Transaction is executed as a single unit.
• If the database was in consistent state before a transaction, then after execution of the transaction also, the database must be in a consistate.
• For example, a transfer of money from one bank account to another requires two changes to the database both must succeed or fail together.

Lock point

• The “Lock Point” is when all locks are held for the whole transaction.
• Binds all of the data used in a transaction together.
• It, therefore, prevents a transaction from being split into parts.