6.Transaction Management,Data ConCurrency and Data Consistency

Transaction Management

v  Logical unit of work that contains one more sql statements

v    A Transaction is an Atomic unit. The Transaction can be either  committed(Apply to the database) or Roll backed(undone from database)

v  Transaction starts with sql statements and ends with Commit or   Rollback

                 Commit

                  Rollback

                  Save point 

                  Transaction Name

            Ex. Fund Transfer.

Data ConCurrency

ü  Multiple users uses same data simultaneously.

ü   Reduce waiting time.

ü   Lock  is a mechanism that provides Maximum concurrent access to the data

Data Consistency

Ø  Each user must see a consistent view of the data, including visible changes made by a user's own transactions and committed transactions of other users.

Ø  Statement Level  Read Consistency

               -Select query without commit of update query

Ø  Transaction Level Read Consistency

     -Update query  without commit, another query wants to update  data means it will block.