Oracle SQL: the Essential Reference

SET TRANSACTION

SET TRANSACTION {READ ONLY | READ WRITE | ISOLATION LEVEL {SERIALIZABLE | READ COMMITTED} | USE ROLLBACK SEGMENT seg_name }

Establishes the current transaction as read-only or read-write or specifies the rollback segment to be used by the transaction.

Keywords

READ ONLY

Specifies that the current transaction is read-only.

READ WRITE

Specifies that the current transaction is read-write.

ISOLATION_LEVEL

Specifies how database modifications are to be handled. SERIALIZABLE means that if an attempt is made to update a row that has been updated and not yet committed by another session, the statement will fail; this situation is consistent with the serializable transaction isolation mode specified in the ANSI SQL-92 standard. READ COMMITTED means that Oracle's default behavior will be in effect, and if a row is locked by another uncommitted transaction, the statement will wait until the row locks are released.

USE ROLLBACK SEGMENT

Assigns this transaction to the rollback segment specified by seg_name. This clause implies READ WRITE and cannot be specified with READ ONLY.

If used, this statement must be the first in your transaction. A transaction is ended with a COMMIT or COMMIT WORK statement.

Example

Specify a rollback segment and perform an update transaction:

SET TRANSACTION
   USE ROLLBACK SEGMENT rbs99;

UPDATE emp
SET SAL = SAL*1.1;

COMMIT;