Heroku, Oink and R14 errors. Can one line of code need 70MB of memory?

Question

I've been somewhat concerned at the number of R14 errors I'm getting on Heroku recently.

I don't know if this has anything to do with using Unicorn. Or having recently installed New Relic or Logentries. I really can't work it out.

I have "installed" Oink and have just received the following analysis but have no read idea how to fully understand what it's trying to tell me.

---- MEMORY THRESHOLD ----
THRESHOLD: 0 MB

-- SUMMARY --
Worst Requests:
1. Nov 13 02:53:51, 70836 KB, messages#getmessagecount
2. Nov 13 02:03:04, 65836 KB, messages#getmessagecount
3. Nov 13 02:21:46, 60236 KB, messages#getmessagecount
4. Nov 13 01:32:47, 6328 KB, messages#deletemessage
5. Nov 13 01:33:43, 6328 KB, locations#sendprofiles
6. Nov 13 01:32:56, 6328 KB, messages#deletemessage
7. Nov 13 01:32:58, 6328 KB, messages#deletemessage
8. Nov 13 01:32:49, 6328 KB, messages#deletemessage
9. Nov 13 01:47:46, 5300 KB, messages#getmessagecount
10. Nov 13 03:09:56, 5300 KB, messages#getmessagecount

Worst Actions:
9, messages#deletemessage
7, messages#getmessagecount
1, locations#sendprofiles
1, photos#photodatarequest
1, messages#getmessages

Aggregated Totals:
Action                      Max Mean    Min Total   Number of requests
messages#getmessagecount    70836   29814   464 208700  7
messages#deletemessage      6328    3016    180 27144   9
locations#sendprofiles      6328    6328    6328    6328    1
photos#photodatarequest     460 460 460 460 1
messages#getmessages        300 300 300 300 1

I'm concerned, as a layman, that my message#getmessagecount is eating a LOT of memory. Is that what the above means?

If so ... the routine is simply:

def getmessagecount

    @messagecount = Message.where(recipient: current_user, messageSysMessCode: 0, messageAdminMessage: false).count

  end

And I have no idea how this could be "leaking" memory.

The graph of memory usage on Heroku over the last day looks like:

I'm using Ruby 2.1.4 and Rails 4.1.7 if that's any help. I'm using two Web dynos and one Worker.

Oh ... and my delete message routine is:

def deletemessage

@message = Message.where(recipient_id: current_user.id, id: params[:messageID]).first
if (@message)
  @message.delete
  @code = "OK"
else
  @code = "Couldn't delete message"
end

end

This is killing my performance (if that's the right thing to say) every 3 hours or so. I have no idea why this is ramping up every 10 minutes (which I hopefully infer from reading the graph). 10 minutes might be significant as I have an iPhone app which is polling the getmessagecount routine every 10 mins with a single test app. I can only wonder what will happen if 10 copies of the app (or 1,000's) start hitting the server?

Any help would be very deeply appreciated.