Author: GuoQiang Li <witgo@qq.com>
Author: witgo <witgo@qq.com>

Closes #929 from witgo/improve_als and squashes the following commits:

ea25033 [GuoQiang Li] checkpoint products 3,6,9 ...
154dccf [GuoQiang Li] checkpoint products only
c5779ff [witgo] Improve ALS algorithm resource usage