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Spring - Database Transaction (Part 1)

We will define a transaction as a unit of work that is made up of a set of operations, against one or more resources, that must be completed in its entirety.

The ACID properties:
Atomic, Consistent, Isolated, Durable Properties.

Atomicity: All individual steps of the transaction must complete. If one step fails, they must all fail or be undone.
consistency: Transactions must also leave any affected resources in a consistent state.
Isolation: Each transaction should operate isolated from each other and also in the required sequence.
Duration: the transactions should be durable.

Transaction propagation:
Each transaction has some attributes associated with it, like its status. This information is stored in what is called the transaction context. This context must be made available to any transaction manager that handles this transaction. The transaction context is associated iwth the thread that is executing.
In the case where there is a remote call when a transaction is active, the transaction context is passes along, propagated, to the remote process.  This allows the remote process to participate in the same transaction.
The propagation behavior is the attribute that can be used to define the scope of your transactions and how multiple transaction will interact with each other.

 Support a current transaction, create a new one if none exists. Analogous to EJB transaction attribute of the same name. This is typically the default setting of a transaction definition.

 Support a current transaction, execute non-transactionally if none exists. Analogous to EJB transaction attribute of the same name.

 Support a current transaction, throw an exception if none exists. Analogous to EJB transaction attribute of the same name.

 Create a new transaction, suspending the current trans- action if one exists. Analogous to EJB transaction attribute of the same name.

 Execute non-transactionally, suspending the current trans- action if one exists. Analogous to EJB transaction attribute of the same name.

 Execute non-transactionally, throw an exception if a trans- action exists. Analogous to EJB transaction attribute of the same name.

 Execute within a nested transaction if a current transaction exists, or behave like PROPAGATION_REQUIRED otherwise. There is no analogous feature in EJB.

Isolation: the isolation attribute allows you to override the default isolation setting of your data source.
 Dirty reads, non-repeatable reads, and phantom reads can occur.
 Dirty reads are prevented; non-repeatable reads and phantom reads can occur.
 Dirty reads and non-repeatable reads are prevented; phantom reads can occur.
 Dirty reads, non-repeatable reads, and phantom reads are prevented.

This flag can be set to true to indicate that the transaction does not modify any persistent state.  This is more of a hint because not all transactional resources can take advantage of this setting. It's particularly useful when using Hibernate because it tells Hibernate not to detect and flush changes within a read-only transaction.

Transaction Demarcation:
Whether you use local or global transactions, you must somehow inform the transaction manager when your transaction begins and when it ends. This is called transaction demarcation and there are two ways to accomplish this. You can either do it programmactically by using JDBC APIs , or you can take advantage of declarative transaction management that is offered by an EJB container as well as by the Spring Framework.

Declarative Transaction provide a very attractive alternative to the programmatic solutions. You can allow a framework to demarcate the transactions not having to include transaction management in your code makes your code much more readable and easier to maintain.


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