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What Is a Transaction
A transaction is a set of related actions. A global transaction is a set of related actions that span multiple programs and resource managers. In this topic, whenever we use the term transaction, we are referring to a global transaction.
A simple example of a transaction is a withdrawal from a bank account, which can be described as a set of actions that changes the state of an account balance (by reducing it). For this transaction, the system must execute a procedure that consists of three operations.
Procedure for Any Transaction |
Procedure for Bank Withdrawal Example |
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1. Verify the activity to be performed |
1. Verify that a withdrawal will be made |
2. Perform the work of the transaction |
2. Withdraw a specified amount from the account |
3. Create a permanent record of the completed work |
3. Update the record of the balance of the account |
These steps are performed by a discrete software module created expressly for the purpose of executing this transaction. The module must also include or use code that launches and ends the transaction. If the code sections that launch and end the transaction are not part of the main transaction software module, then they are usually packaged together in a separate module.
A transaction coordinator is a software module that executes the logic to manage a transaction among all participating resources.
What Are the ACID Properties
When a transaction such as a bank withdrawal is performed, it is imperative that all its constituent operations either succeed or fail together. Consider the problems that can occur if one operation in a transaction succeeds while another operation in the same transaction fails: a bank that allows a customer to withdraw money without recording the reduced balance in an updated account record will not stay in business for long!
A transaction that adheres to the rule that all constituent operations either succeed or fail is characterized by atomicity. The BEA Tuxedo system requires all transactions to be characterized by atomicity and three related attributes: consistency, isolation, and durability. These four attributes are known collectively as the ACID properties of transactions performed within the BEA Tuxedo system.
ACID Properties of BEA Tuxedo Transactions
How a Transaction Succeeds or Fails
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Copyright © 2000 BEA Systems, Inc. All rights reserved.
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