Specifies the transaction isolation levels that provide the necessary consistency and concurrency control between transactions in the job and other transactions for optimal performance.
Because Oracle does not prevent other transactions from modifying the data read by a query, that data may be changed by other transactions between two executions of the query. Thus, a transaction that executes a given query twice may experience both nonrepeatable reads and phantoms. Use one of the following transaction isolation levels:
Read-only. Sees only those changes that were committed when the transaction began. This level does not permit INSERT, UPDATE, and DELETE statements
Read Committed. Takes exclusive locks on modified data and shareable locks on all other data. Each query executed by a transaction sees only data that was committed before the query (not the transaction) began. Oracle queries never read dirty, that is, uncommitted data. This is the default.
Serializable. Takes exclusive locks on modified data and sharable locks on all other data. It sees only those changes committed when the transaction began plus those made by the transaction itself through INSERT, UPDATE, and DELETE statements. Serializable transactions do not experience nonrepeatable reads or phantoms.