Persistent Messages Published to Topics
Persistent messages published to a topic are written to disk only if that topic has at least one durable subscriber or one subscriber with a fault-tolerant connection to the EMS server.
In the absence of a durable subscriber or subscriber with a fault-tolerant connection, there are no subscribers that need messages resent in the event of a server failure. In this case, the server does not needlessly save persistent messages. This improves performance by eliminating the unnecessary disk I/O to persist the messages.
This behavior is consistent with the JMS specification because durable subscribers to a topic cause published messages to be saved. Additionally, subscribers to a topic that have a fault-tolerant connection need to receive messages from the new active server after a failover. However, non-durable subscribers without a fault-tolerant connection that re-connect after a server failure are considered newly created subscribers and are not entitled to receive any messages created prior to the time they are created (that is, messages published before the subscriber re-connects are not resent).