Imagine that you had an unbounded amount of persistent RAM. How would you access the data within it? SQL?
Discussion
SQL is never the answer
It sometimes is! Not in this case. Modern languages (e.g. Clojure) have good facilities for mapping, filtering, and reducing data in memory.
Redis?
Oracle TimesTen or SAP HANA or some type of DBMS that supports in-memory databases or caching mechanisms
Graph-like structure using pointer hops