The jPOS QMUX service uses the Space (usually the default global space) in order to communicate with other components such as the ChannelAdaptor or QServer using its in and out queues. But in addition, it implements the MUX interface by storing selected parts of a request message (known as the QMUX key), as shown in the picture below:
In high traffic systems, with many QMUXes, every thread waiting for a response would wake up, albeit for a tiny little while, when something happens in the space. This small patch done in 1.9.7 keep using the global space for the QMUX in and out queues, but uses an internal Space (currently a TSpace) to perform the key-matching dance.
The change should be transparent for most users, but we've seen some implementations out there that dangerously peek and poke our entries in the Space, and actually this patch, in addition to improve performance, intend to discourage such use in the future (by not exposing the internal space to other components). But anyway, for backward compatibility, we honor a new property reuse-space that if set to true, would revert to the old implementation, using the global space.