Transaction: data base for money transactions, railway reservation

Transaction: Transaction is a
group of sql (DML) statements which are used to perform certain combination of
operations like write, update etc. into one unit to make the consistency of
data. They are used to perform multiple actions if and only if all the
operations can be performed else none of the action or operation should not be
done and the database should not affect i.e; the transaction is ROLLBACK. If
all the operations are performed successfully than it will be save to database
by issuing the COMMIT command. There is a Transaction log which are used to change
the database to original state in case of any failure occurred. One has to
design the transaction in such way that it ensure the ACID properties. The real
scenarios where Transactions are used are Bank data base for money
transactions, railway reservation etc. 
Transaction is an automatic work with respect to recovery and
consistency.

Structure of a Transaction:

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Transaction starts with BEGIN
TRANSACTION followed by SQL statements and then COMMIT TRANSACTION, ROLLBACK
TRANSACTION. Transactions can be nested.

Example of transaction of bank transaction using TRY catch block.

 

BEGIN TRANSACTION

BEGIN TRY

UPDATE account SET total=total+5000.0 WHERE account_id=1337;

UPDATE account SET total=total-5000.0 WHERE account_id=45887;

COMMIT

 

END TRY

BEGIN CATCH

PRINT ‘Transaction rollback’

ROLLBACK

END CATCH

 

GO

When we execute this procedure if the two commands
execute successful then transaction Commit else it goes to CATCH block and
performs rollback

 

Transaction Processing:

Transaction processing gives a
scheme which is used to check the progress and controls the execution of
transaction programs. Transaction processing mainly used in mission-critical
applications which requires large amount of parallel users with minimum
downtime.  Proper use of Transaction
Processing results the controlling the execution of several applications which
are executing parallel. Transaction processing ensures the ACID properties over
different databases this can be done by using two-phase COMMIT. Transaction
processing system is best used if an application requires online access and
also if there is a modification on different databases.

                                             

Local Transaction: When the
transaction is limited to only single database or resource is called Local
Transaction and all the operations will commit at the end point of the
transaction.

Distributed Transaction:

Unlike to local transaction which
are limited to specific resource distributed transactions extend across
multiple databases or resources. It is similar to local transaction where at
the end point of the transaction it should be either committed or roll backed.
If we have a situation where network failure occurs then but unfortunately in
place of rollback all the transactions the data in one of the database or
resource is committing this can happen due to many reasons to minimize these
type of risk distributed transaction uses TWO –PHASE COMMIT process.

Implicit transaction contains
only one statement of either INSERT, UPDATE, DELETE etc. After connecting to
the database then if we perform or execute any DML statements then changes are
made and saved to database automatically. This happens since the connection is
in auto commit transaction mode. If you don’t want to save any changes until
unless you specifies the COMMIT or ROLLBACK then we can use Implicit
Transaction. Using Implicit Transaction the transactions remains in effect
until the user issues the COMMIT or ROLLBACK commands.

Explicit transaction contains
multiple statements with BEGIN indicates start the transaction and END
indicates end the transaction. Using explicit transaction the transaction is
controlled by the user when the transaction is going to start and when it should
ends. These are also called user-defined transactions. 

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