It is very etiolated plant...all succulents (cacti are succulents too) need good drainage and good light exposure = that means lots of sunlight (hours a day) for most of them. If they do not have adequate light, they grow in shape very different than plant should have, with weak stems, often very pale color. All thin growth of your plant happened under poor light; it should be more-or-less same thickness as the thickest par, all over. In simple words - chubbier and shorter :)

I think it might be Euphorbia mammillaris. As Rina said, and to paraphrase the last words of Johann Wolfgang von Goethe, "More light!"