Each queue that is created is automatically bound to the default (direct)
exchange with a routing key that matches the queue name. When the queue is
deleted, the queue is correctly removed from the binding map, but the mapping
from routing key to queues is not removed even when there are no queues bound
to the routing key.
In a case where thousands of uniquely named queues are created and deleted as
transient storage, the memory usage of the broker will continue to grow as the
default exchange's routing key map continues to grow.