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Distributed transaction model-oocomputerworld

 Distributed transaction model

Distributed transaction model:- To access the various data items in a distributed system is usually e accomplished through transaction there are two type of transaction that we need to consider

  1. The local transaction
  2. The Global transaction 

 The local transaction:- The local transaction are those that access and update data is only one local database. 

The global transaction:- global transaction are those that access and update data in several local database in the case of global transaction the task is more complicated since several nodes may be participating in execution the failure of a communication link connecting these nodes may result in erroneous computation.

 System structure :- Each node has its oven local transaction manager whose function is to ensure those transaction that execute at that site. The various transaction manager corporate to execute global transaction. To understand how such a manager can be implemented we define and abstract model of a transaction system each node of the system contains two sub system. 

The transaction manager :- The transaction manager manages the execution of those transaction that access data stored  in a local node.

 Transaction coordinator :- The transaction coordinator coordinates the execution of various transaction both local and global.

 The structure of a transaction manager is similar to centralized system and each transaction manager is responsible for maintaining a log  for recovery purpose and execution of the transaction at the node.

 Transaction coordinator is responsible for starting the execution of the transaction and breaking transaction into a number of such transaction and distributing these Sub transaction to the appropriate nodes for execution.

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