I have a successful installation in Heroku using ClearDB MySQL and it works all perfect but some times. It get misconfigured and I have to “re-install” using the same DB so I dont miss any data but there is a period when Piwik is inactive.
I dont know why is happening but It might be because files written in installation are not in pushed git repository. Heroku might restart sometimes with the pushed version so written files in installation might be lost.
I have just successfully deploy in heroku just as we commented:
Add to your repo /config/config.ini.php your DB settings and also set session_save_handler = dbtable not to lose session info when heroku starts your dyno in another machine (at least once per day)