Spring Transaction

Transaction comprises of a unit of work against a database. Transaction provides “all or noting” preposition unit of work performed entirely committed or rollback.

Unit of work: consider to transfer account balance from account A to account B we have to debit account A and credit account B and this is a unit of work performed to do transfer.

Acronym ACID describes the nature or properties for transaction.

•   Atomic: All of the operations in a transaction happen or none of them happen.  
•   Consistent: After a successful or failed transaction system is left in a consistent state.
• Isolation: it is about concurrent read write if two or more transaction progressing at time. 
•  Durable: after a successful transaction data is persisted permanently.  

Transaction attributes:

• Propagation

1.     PROPAGATION_REQUIRED: transaction already exists then the code will use it otherwise a new transaction is created. This is the default.

2.     PROPAGATION_SUPPORTS: transaction exists then the code will use it, but the code does not require a new one.

3.     PROPAGATION_MANDATORY: Participates in an existing transaction, however if no transaction context is present then it throws a TransactionRequiredException.

4.     PROPAGATION_REQUIRES_NEW: new transaction and if an existing transaction is present then it is suspended. When the new transaction is complete then the original transaction resumes.

5.     PROPAGATION_NOT_SUPPORTED: operations needs to be performed non-transitionally.

6.     PROPAGATION_NEVER: code cannot be invoked within a transaction. if an existing transaction is present then an exception will be thrown.

7.     PROPAGATION_NESTED: code is executed within a nested transaction if existing transaction is present; if no transaction is present then a new transaction is created.

• Isolation

1.     ISOLATION_DEFAULT: Use the isolation level of the underlying database. This is the default.

2.     ISOLATION_READ_UNCOMMITTED:  dirty reads, phantom reads and non-repeatable reads.

3.     ISOLATION_READ_COMMITTED: prevents dirty reads but allows phantom reads and non-repeatable reads.

4.     ISOLATION_REPEATABLE_READ: prevents dirty reads and non-repeatable reads but allows phantom reads.

5.     ISOLATION_SERIALIZABLE: prevents dirty reads, non repeatable reads and phantom reads.

Dirty Reads- Dirty reads occur when transaction B reads data that has been modified by transaction A but not committed. The problem occurs when transaction A rollbacks the transaction, in which case the data read by transaction B will be invalid.

Non Repeatable Reads- Non-repeatable reads happen when a transaction fires the same query multiple times but receives different data each time for the same query.

Phantom Reads - Phantom reads occur when the collection of rows returned is different when a same query is executed multiple times in a transaction.

• Read only: The read only attribute specifies that the transaction is only going to read data from a database. by default false.
• Rollback rule: specify that transactions roll back on certain exceptions and do not rollback on other exceptions.By default RuntimeException.
• Timeout: Timeout specifies the maximum time allowed for a transaction to run then rolled back.

Spring Transaction supports:

• It offers both programmatic and declarative transaction.
• Declarative transaction can be used in stand-alone application unlike EJB.
• Support wide range of transactional manager,.
• Spring transactions are good at application using single database. I multiple databases access required have to use XA transaction of JTA.

Spring transaction managers: soring does not manage transaction directly rather delegate the responsibility to configured platform specific transaction manager.

JDBC	DataSourceTransactionManager
Hibernate	HibernateTransactionManager
JDO	JdoTransactionManager
JTA	JtaTransactionManager
JPA	JpaTransactionManager

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