How do you control the transaction isolation level in JDBC? — Java JDBC Interview Question #25

The transaction isolation level in JDBC can be controlled by using the Connection object’s setTransactionIsolation() method. The transaction isolation level defines how concurrent transactions access shared data and what locking mechanisms and constraints are used to maintain the consistency of the data.

JDBC provides four levels of transaction isolation that can be set using the setTransactionIsolation() method:

1. TRANSACTION_READ_UNCOMMITTED: This is the lowest level of transaction isolation where a transaction can read uncommitted changes by other concurrent transactions. This level of isolation is not recommended as it can lead to dirty reads or non-repeatable reads.

    connection.setTransactionIsolation(Connection.TRANSACTION_READ_UNCOMMITTED);

2. TRANSACTION_READ_COMMITTED: In this level of transaction isolation, a transaction can only read committed changes by other concurrent transactions. This level eliminates the possibility of dirty reads, but non-repeatable reads and phantom reads may still occur.

    connection.setTransactionIsolation(Connection.TRANSACTION_READ_COMMITTED);

3. TRANSACTION_REPEATABLE_READ: This level of transaction isolation ensures that a transaction can only read data that hasn’t changed since the transaction started. This level eliminates the possibility of dirty reads and non-repeatable reads, but phantom reads may still occur.

    connection.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);

4. TRANSACTION_SERIALIZABLE: This is the highest level of transaction isolation where the transactions are executed serially i.e. one after the other. This level ensures the highest level of data consistency but results in slower performance and can cause deadlocks.

    connection.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);

It is important to note that different database vendors may have different default transaction isolation levels, and some may not support all four levels. Therefore, it is important to consult the database’s documentation for details on how to set and configure transaction isolation levels.