Isolation and Propagation in Spring Transaction - Sudipta13samanta/Spring GitHub Wiki

Propagation is the ability to decide how the business methods should be encapsulated in both logical or physical transactions.

• PROPAGATION_REQUIRED, means that the same transaction will be used if there is an already opened transaction in the current bean method execution context.
• PROPAGATION_REQUIRES_NEW, means that a new physical transaction will always be created by the container.
• PROPAGATION_MANDATORY, states that an existing opened transaction must already exist. If not an exception will be thrown by the container.
• PROPAGATION_NOT_SUPPORTED, will execute outside of the scope of any transaction. If an opened transaction already exists it will be paused.
• PROPAGATION_SUPPORTS, will execute in the scope of a transaction if an opened transaction already exists. If there isn't an already opened transaction the method will execute anyway but in a non-transactional way.
• PROPAGATION_NEVER, states that an existing opened transaction must not already exist. If a transaction exists an exception will be thrown by the container.
• PROPAGATION_NESTED, makes nested Spring transactions to use the same physical transaction but sets savepoints between nested invocations so inner transactions may also rollback independently of outer transactions.

Isolation level defines how the changes made to some data repository by one transaction affect other simultaneous concurrent transactions, and also how and when that changed data becomes available to other transactions. When we define a transaction using the Spring framework we are also able to configure in which isolation level that same transaction will be executed.

• READ_UNCOMMITTED isolation level states that a transaction may read data that is still uncommitted by other transactions.
• READ_COMMITTED isolation level states that a transaction can't read data that is not yet committed by other transactions.
• REPEATABLE_READ isolation level states that if a transaction reads one record from the database multiple times the result of all those reading operations must always be the same.
• SERIALIZABLE isolation level is the most restrictive of all isolation levels. Transactions are executed with locking at all levels (read, range and write locking) so they appear as if they were executed in a serialized way.