# Configuring isolation levels

If a connection does not specify its isolation level, it inherits the default isolation level for the Derby system. The default value is `CS`.

When set to `CS`, the connection inherits the TRANSACTION_READ_COMMITTED isolation level. When set to `RR`, the connection inherits the TRANSACTION_SERIALIZABLE isolation level, when set to `RS`, the connection inherits the TRANSACTION_REPEATABLE_READ isolation level, and when set to `UR`, the connection inherits the TRANSACTION_READ_UNCOMMITTED isolation level.

To override the inherited default, use the methods of java.sql.Connection.

In addition, a connection can change the isolation level of the transaction within an SQL statement. For more information, see "SET ISOLATION statement" in the Java DB Reference Manual. You can use the WITH clause to change the isolation level for the current statement only, not the transaction. For information about the WITH clause, see "SELECT statement" in the Java DB Reference Manual.

In all cases except when you change the isolation level using the WITH clause, changing the isolation level commits the current transaction. In most cases, the current transaction is committed even if you set the isolation level in a way that does not change it (that is, if you set it to its current value). See Isolation levels and concurrency for details.

Note: For information about how to choose a particular isolation level, see "Shielding users from Derby class-loading events" in Tuning Java DB and Multi-thread programming tips.
Parent topic: Locking, concurrency, and isolation
Related concepts
Isolation levels and concurrency
Lock granularity
Types and scope of locks in Derby systems
Deadlocks