want proper index

proxy.rb

    def pick(provider, current_proxy=nil)
      _accessible = {"unaccessible" => nil}
      _not_banned = []
      _not_banned << {"banned.#{provider}" => nil }
      _not_banned << {"banned.#{provider}" => { '$lt' => BANNED_UNTIL[BANNED_SECONDS] }}

      _different_subnet = {}
      if current_proxy
        _different_subnet = {
          :subnet_int => {'$ne' => current_proxy[:subnet_int]}
        }
      end

      _search_conditions = {
        "$and" => [
          _accessible,
          _different_subnet,
          {'$or' => _not_banned }
        ]
      }
      _sort_conditions = {"used_at.#{provider}" => 1}

      proxy = find_one(_search_conditions, :sort => _sort_conditions)
      raise NoProxyLeft, "sorry, all proxies are banned by #{provider}" unless proxy

      proxy[:used_at] ||= {}
      proxy[:used_at][provider] = Time.now
      proxy.update

      proxy
    end