Since upgrading to app-engine-patch 1.0 you have to run instead of the dev server. However, I hadn’t bothered to trace down why the –datastore_path=filename.datastore parameter wasn’t working until today.

For informal parameters, the name and values are not added separately. So you can work around this by dropping the = between –datastore_path and –history_path. Otherwise the datastore is put in /tmp on OSX and that gets erased when you reboot.