Create a C++ client that receives lots and lots of messages. Call session.acknowledge(message) on each message. If you don't call session.sync() periodically, the client application's memory usage will increase over time. Most of the memory allocated appears to be coming from qpid::client::amqp0_10::AcceptTracker::accept(qpid::framing::SequenceNumber id, qpid::client::AsyncSession& session). It looks like the broker doesn't send completions for the message acknowledgements, or if it does, not very frequently.