This property is applicable only for an enqueue operation.
Possible values are:
ORAAQ_ENQ_IMMEDIATE (1)
The enqueue operation constitutes a transaction of its own. Set this property to make the message visible immediately after the enqueue operation.
ORAAQ_ENQ_ON_COMMIT (2) (Default)
The enqueue is part of the current transaction, and the message is visible only after the transaction commits.