Comment 2 for bug 894105

I got Tom to run the following query on the U1 account database:

SELECT claimed_id, count(*), max(user_id) - min(user_id) AS user_id_spread
  FROM django_openid_auth_useropenid
  GROUP BY claimed_id having count(*) > 1;

The results are here: https://pastebin.canonical.com/56463/

The user_id_spread was usually only 1 (i.e. claimed_id held by two sequentially created accounts), and at most was 3. So it most likely represents race conditions on account creation (maybe people hitting reload in the browser). With the constraint in place, the second account creation should fail, but the user should still be able to log in to the first account created.