Transactions

Transactions

1. @Transactional

   • Propagation Type
     • MANDATORY
       • Support a current transaction, throw an exception if none exists.
     • NESTED
       • Execute within a nested transaction if a current transaction exists
     • NEVER
       • throw an exception if a transaction exists.
     • NOT_SUPPORTED
       • suspend the current transaction if one exists.
     • REQUIRED
       • Support a current transaction, create a new one if none exists.
     • REQUIRES_NEW
       • Create a new transaction, and suspend the current transaction if one exists.
     • SUPPORTS
       • Support a current transaction, execute non-transactionally if none exists.
   • Isolation Level
     • DEFAULT
     • READ_COMMITTED
       • keeps write locks
       • Locks are released as soon as the SELECT operation is performed
       • range-locks are not managed
       • Restricts dirty read
     • READ_UNCOMMITTED
       • lowest isolation level
       • may see not-yet-committed changes made by other transactions.
     • REPEATABLE_READ
       • keeps read and write locks
       • range-locks are not managed
     • SERIALIZABLE
       • This is the highest isolation level.
       • requires read and write locks
       • Also range-locks must be acquired
       • Phantom reads doesnt ocurrs
   • Time out
   • readOnly flag
     • Optimization in some cases
       • when you are using Hibernate
     • Provide safe guard
       • Oracle and some other databases
   • Rollback rules
   • by default, rollback happens for unchecked exceptions only (Runtime)
   • Spring create a proxy for this class
     • To inject transactional logic before and after the method being invoked
     • if the bean is implementing an interface
       • any self-invocation calls will not start any transaction
         • even if the method is annotated with @Transactional.
   • <tx:annotation-driven />
     • Enables Transactions

2. Global Transactions

   • work with multiple transactional resources
     • Multiples Databases?

3. Local Transactions

   • Local transactions are resource-specific
     • JDBC connection

4. PlatformTransactionManager (Interface)

   • commit(TransactionStatus ts)
   • rollback(TransactionStatus status)
   • TransactionStatus getTransaction(TransactionDefinition definition)
   • throw a TransactionException
     • RuntimeException

5. TransactionTemplate

   • Is a template emplates such as the JdbcTemplate
   • Need a TransactionCallback implementation
     • will contain code that you need to have execute in the context of a transaction
   • Propagation mode, the isolation level, the timeout, can be set programmatically
     • Or in configuration
   • they are threadsafe
   • Simplifies programmatic transaction demarcation and transaction exception handling.
   • the central method is execute(TransactionalCallback)

6. Spring AOP is used to apply the transaction

   • if an target method1, calling an method2 directly in the target object
     • will not be applied by the proxy to the method2