About Message Ordering

Message ordering determines the order in which messages are dequeued. Oracle Streams Advanced Queuing (AQ) provides the following options for message ordering:

• Enqueue time: Messages are dequeued in the same order that they were enqueued. This option is sometimes called first in first out (FIFO) ordering. For example, banking applications often use this ordering so that financial transactions are always ordered according to the time when they occurred.

• Priority: A priority is specified for messages during enqueuing, and messages are dequeued based on their priority. For example, shipping companies might use this ordering for messages because some packages have higher priority than others.

• Commit time: Messages are dequeued based on when the transaction that enqueued the messages committed. Commit-time ordering is typically used when the messages result in database changes with transaction dependencies. For example, an application that handles sales for a company might use commit-time ordering when the messages result in changes to a number of database tables that have dependencies.