1. A method for managing messages in a database system, the method comprising the computer-implemented steps of: determining whether an amount of available space in a message queue that is disposed in a volatile memory of the database system is less than a specified amount; if the amount of available space in the message queue is less than the specified amount, then moving a message from the message queue in the volatile memory to a persistent message queue disposed on a non-volatile storage in the database system, and generating and storing in the message queue, message header data that identifies that the message is stored in the persistent message queue.