09-08-2012, 04:55 PM
TRANSACTION PROCESSING SYSTEMS
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Transaction Processing Systems
“Collection of operation that form a single logical unit of work are called TRANSACTION”. Often, a collection of several operation on the database appears to be a single unit from the point of view of the database user. For example, a transfer of funds from a checking account to a saving account is a single operation from the customer standpoint; within the database system,however, it consist of several operations. Clearly, It is essential that all these operation occure, or that, in case of a failure, none occure. It would be unacceptable if the checking account is debited, but the saving account were not credited. A database system must ensure proper execution of transaction despite failures-either either the entire transaction execute , or none of it does. Furthermore, it must manage concurrent execution of transaction in a way that avoid the introduction of inconsistency. In our funds-transfer example, a transaction computing the customer’s total money might see the checking account balance before it is debited by the funds-transfer transaction, but see the saving balance after it is created. As a result, it would obtain an incorrect result.
Transaction Concept
A Transaction is a unit of program execution that accesses and possibly updates various data items. Usually a transaction is initiated by a user program written in a high level data manipulation language (for example ,SQL,C++,JAVA) where it is delimited by statements (for function calls) of the form begin transaction and end transaction. The transaction consist of all operation executed between the being transaction and end transaction .
[attachment=30850]
Transaction Processing Systems
“Collection of operation that form a single logical unit of work are called TRANSACTION”. Often, a collection of several operation on the database appears to be a single unit from the point of view of the database user. For example, a transfer of funds from a checking account to a saving account is a single operation from the customer standpoint; within the database system,however, it consist of several operations. Clearly, It is essential that all these operation occure, or that, in case of a failure, none occure. It would be unacceptable if the checking account is debited, but the saving account were not credited. A database system must ensure proper execution of transaction despite failures-either either the entire transaction execute , or none of it does. Furthermore, it must manage concurrent execution of transaction in a way that avoid the introduction of inconsistency. In our funds-transfer example, a transaction computing the customer’s total money might see the checking account balance before it is debited by the funds-transfer transaction, but see the saving balance after it is created. As a result, it would obtain an incorrect result.
Transaction Concept
A Transaction is a unit of program execution that accesses and possibly updates various data items. Usually a transaction is initiated by a user program written in a high level data manipulation language (for example ,SQL,C++,JAVA) where it is delimited by statements (for function calls) of the form begin transaction and end transaction. The transaction consist of all operation executed between the being transaction and end transaction .