It has been recently established that joint design of content delivery and
storage (coded caching) can significantly improve performance over conventional
caching. This has also been extended to the case when content has non-uniform
popularity through several models. In this paper we focus on a multi-level
popularity model, where content is divided into levels based on popularity. We
consider two extreme cases of user distribution across caches for the
multi-level popularity model: a single user per cache (single-user setup)
versus a large number of users per cache (multi-user setup). When the capacity
approximation is universal (independent of number of popularity levels as well
as number of users, files and caches), we demonstrate a dichotomy in the
order-optimal strategies for these two extreme cases. In the multi-user case,
sharing memory among the levels is order-optimal, whereas for the single-user
case clustering popularity levels and allocating all the memory to them is the
order-optimal scheme. In proving these results, we develop new
information-theoretic lower bounds for the problem.Comment: 13 pages; 2 figures. A shorter version is to appear in IEEE ISIT 201