HornetQ supports many message queues with each queue containing millions of messages. The HornetQ server runs with limited memory thereby making it difficult to store all message queues in memory at one time.
Paging is a mechanism used by the HornetQ server to transparently page messages in and out of memory on need basis in order to accomodate large message queues in a limited memory.
HornetQ starts paging messages to disk, when the size of messages in memory for a particular address exceeds the maximum configured message size.
HornetQ paging is enabled by default.