I checked into this, and this is a per-user history entry that verifies we looked up their avatar.
context "a user who has been checked for a custom avatar" do
UserHistory.create!(action: UserHistory.actions[:checked_for_custom_avatar], target_user_id: user.id )
# Finally, we don't check users whose avatars haven't been examined
return unless UserHistory.exists_for_user?(@user, :checked_for_custom_avatar)
Which logs are you referring to? How are you exporting the per-user history logs? These are not under admin/logs AFAIK.
Also do you have 45,525 users? There should only be one of these records per user.
edit: confirmed, we have a zillion of these rows as well in Staff Action Logs. That stopped about 5-27-2014. Looks like some kind of bug in the export process and/or an issue with the number of those records in the individual user histories. @techapj is having a look.