Since I am using batch rendering, so I should pack every render units can be batched into one big VBO. But, what if I am in a case where render units are dynamically changed, some new units are added in, and some units are subtracted out. So I should reconstruct my VBO again and again in very frame. So here is the question.
Should I allocate a big enough storage in the first time and update the data in it, and only reallocate when run out of the storage, or allocate storage according to the size on demand in each frame?