Design a many-to-many table for scale I am thinking about scaling issues with many-to-many join tables.

I have a constructed example as following:


Many users have many wishlists.
On every wishlist are many items.


If I scale this table to million of users the wishlist_items table 
will get very big:


1000000 users
100 wishlists for every user
around 1000-10000 items on every wishlist (bad example, but you get the point)


Therefore table size for the join table will be:

users * wishlist_per_user * items_per_wishlist


I think this is a very common situation in RDBM design. I am afraid that this users * wishlist_per_user * items_per_wishlist relation will grow out of bound. 

Are there any similar experiences with such big tables and how to query them fast? How would I design my tables to prepare for better scaling?
I think using separate wishlists for separate users will be your best option. It will be efficient and will not contain millions of rows.