What is the Spring transaction isolation mechanism?

The Spring transaction isolation mechanism is a way to control the level of interference between concurrent transaction operations. It defines the isolation level of database transactions in a concurrent environment to ensure consistency and reliability of transaction operations.

There are several common transaction isolation levels used in the Spring framework.

1. DEFAULT: Use the default transaction isolation level of the database. Typically this is the database’s default level, such as REPEATABLE_READ for MySQL.
2. READ_UNCOMMITTED: The lowest isolation level that allows transactions to read uncommitted data changes. This may lead to issues such as dirty reads, non-repeatable reads, and phantom reads.
3. READ_COMMITTED: Ensures that one transaction can only read data that has been committed by another transaction. This prevents dirty reads, but may still allow for non-repeatable reads and phantom reads.
4. REPEATABLE_READ: Ensures that during a transaction, multiple reads of the same data will be consistent, avoiding dirty reads and non-repeatable reads issues, but may still encounter phantom reads.
5. SERIALIZABLE is the most strict isolation level, preventing concurrency issues by forcing transactions to be executed serially. It ensures that problems like dirty reads, non-repeatable reads, and phantom reads do not occur, but it has lower performance.

The choice of Spring transaction isolation level should be based on specific business needs and database support, typically defaulting to the READ_COMMITTED level.