ActiveMQ in Action–How are message stored by ActiveMQ?

• Messages sent to queues and topics are stored differently, because there are some storage optimizations that can be made with topics that don’t make sense with queues.
• Queues
• Straightforward
• FIFO
• Only when that message has been consumed and acknowledged can it be deleted from the broker’s message store.
• Topics
• Durable subscribers to a topic.
• Each consumer gets a copy of the message.
• Only one copy of message is stored by the broker
• A durable subscriber object in the store maintains a pointer to its next stored message and dispatches a copy of its consumer.
• A message can’t be deleted from the store until it’s been successfully delivered to every interested durable subscriber.