JDBC supports four different transaction isolation levels which determine how transactions should be locked and isolated in a database:
1. READ_UNCOMMITTED: This is the lowest isolation level which allows transactions to read uncommitted data from other transactions, which can lead to dirty reads, non-repeatable reads, and phantom reads. The benefit of this isolation level is that it provides the highest level of concurrency as transactions are not locked for read operations.
2. READ_COMMITTED: In this isolation level, transactions can only read committed data from other transactions. This eliminates dirty reads but can still result in non-repeatable reads and phantom reads. The benefit of this isolation level is that it allows for higher concurrency than the next level.
3. REPEATABLE_READ: This isolation level ensures that a transaction always reads the same data for a given query, even if other transactions commit or update data in the meantime. This eliminates non-repeatable reads but can still result in phantom reads. The drawback of this isolation level is that it can lead to higher levels of contention and decreased concurrency.
4. SERIALIZABLE: This is the highest isolation level which ensures that transactions are completely isolated from one another so that no dirty reads, non-repeatable reads, or phantom reads can occur. The drawback of this isolation level is that it can result in lower concurrency since transactions are locked for read and write operations.
In summary, the choice of transaction isolation level depends on the specific requirements of the application. For example, an application with a high frequency of read operations may benefit from READ_UNCOMMITTED, while an application that requires the highest level of data consistency may need to use SERIALIZABLE. It’s important to carefully consider the trade-offs of each isolation level and choose the one that best fits the application’s needs.