yes. AMQ will try and utilise it available resources.
Checkout the default configuration[1], the systemUsage section:

 <!--  The maximum about of space the broker will use before slowing
down producers -->
        <systemUsage>
            <systemUsage>
                <memoryUsage>
                    <memoryUsage limit="20 mb"/>
                </memoryUsage>
                <storeUsage>
                    <storeUsage limit="1 gb" name="foo"/>
                </storeUsage>
                <tempUsage>
                    <tempUsage limit="100 mb"/>
                </tempUsage>
            </systemUsage>
        </systemUsage>


This sets the default limits for the system as a whole. The
Destination specific policies allow more fine grained control.

see also: http://activemq.apache.org/javalangoutofmemory.html

[1] http://svn.apache.org/repos/asf/activemq/trunk/assembly/src/release/conf/activemq.xml

2008/9/2 lucidm <brandon@lucidmedia.com>:
>
> I have a simple question about memory usage in ActiveMQ 5.1.  By default, the
> bin/activemq script sets the maximum Java heap size at 512mb.  I have
> noticed that if I do not specify a systemUsage / memoryUsage limit to
> something less than 512mb, my in-memory queue will grow until the entire
> ActiveMQ server becomes unstable.  I start getting OutOfMemory exceptions
> regarding the system's inability to launch GC.  Is this normal?  Do I need
> to manually manage the configuration for the memory usage across all of my
> queues to make sure that the system will not become unstable when one of my
> queues fills up?
>
> Thanks,
> ~Brandon.
> --
> View this message in context: http://www.nabble.com/Memory-Usage-Question-tp19274787p19274787.html
> Sent from the ActiveMQ - User mailing list archive at Nabble.com.
>
>