The subscription emails script still uses very much memory (around 5 GB). There was some discussion about possible improvements yesterday (http://chatlogs.musicbrainz.org/musicbrainz-devel/2015/2015-02/2015-02-10.html#T19-06-16-540578):

• Process editors in smaller batches.
• Don't load subscriptions for editors without email address, as they won't be sent an email anyway.
• Retrieve the list of entities with more than, e.g., two subscribers from the database before the run, and only cache those.
• Only store aggregate information about the edits (number of open ones, number of applied ones).
• Perhaps even: Only load aggregate information from the DB to begin with.