| <div class="wiki-content maincontent"><p>Nearly all messaging systems (certainly open source ones) hold either a copy of a persistent message or a reference to a persisted message in memory. This is primarily to try and improve performance, but it also can significantly decrease the complexity of implementation. In fact ActiveMQ version 4 and below worked this - way - by holding references to persisted messages in memory.</p><p>However there is a limitation to this approach, no matter how much memory you have at your disposal, you will hit a limit to the number persistent messages a broker can handle at any particular time.</p><p>To get around this limitation, ActiveMQ introduced a paging cache - for all message stores (except the memory store) to get the best of both worlds - great performance and the ability to hold 100s of millions of messages in persistent store. ActiveMQ is <strong>not</strong> limited by memory availability, but by the size of the disk available to hold the persistent messages.</p><p>For more information see: <a shape="rect" href="message-cursors.html">Message Cursors</a></p></div> | |