I must do 5M (5 000 000) super-columns, or ~25M (5M * 5) regular composite-key columns. Alternatively I need to use ordered partitioner.
What is exact downside of too many super columns? and why I should avoid them, because if i do composite keys, it is "home-made" super column, and all keys will be still there.
Super columns are deprecated and will be replaced ultimately by composites. This is reason enough to avoid them. Plus there is a performance hit with SCs, and the codebase for them is generally not as well traveled.