Reason that this is in the json library and not in the local proxy library is exactly the cost of building the cache. My anecdotal evidence so far is that doing the json loading is much slower than building the cache. Building the cache takes about 0.5s for 14k songs, though I have a fairly beefy machine. As for the sort, we are not sorting the tracks, as this is really a ``sorted(self._tracks.keys())``, so this is just a list of uris.