PL/SQL APIs perform enqueue and dequeue operations for Java Message Service (JMS) payload in Transactional Event Queues. Similarly, the PL/SQL Array APIs are exposed to Transactional Event Queues JMS users. Since JMS supports heterogeneous messages in a single JMS destination, dequeue gets one of the five JMS message types back, but cannot predict what is the type of the next message received. Therefore, it can run into application errors with PL/SQL complaining about type mismatch. Oracle suggests that the application always dequeue from Transactional Event Queues using the generic type
Customers can use PL/SQL APIs to enqueue and dequeue JMS payloads in Transactional Event Queues to avoid client-server round trips.