Chapter 6, Problem 6.27RQ

Program Plan Intro

Transaction:

A transaction is a small set of changes which must be made to the database. The transaction done to the database may or may not affect the changes to the content of the database. The execution takes place as a single unit.

Transaction isolation level:

The transaction isolation level gives the measure of the extent to which transaction isolation succeeds.

• This process is defined by the presence or the absence of the phenomena like dirty read, non-repeatable reads, phantoms.
• These problems occur while reading the data from the database.

Dirty Read:

A dirty read occurs when a transaction reads data from a row which has been changed, but the changes made to the data have not been committed. When the changes have been rolled back, the transition holds an incorrect data.

“Non-repeatable” Read:

The non-repeatable read occurs when a transaction reads data from the same row twice; but gets different data each time. It returns different row values or shows that the row has been deleted.

Phantom read:

A phantom read occurs when transaction reads the data again and discovers new rows which have been inserted by a committed transaction.