From the website:
Ehcache Search is an addition to the core Ehcache API that lets you query, search and analyze billions of cache entries in memory, with results to complex searches returned in less than a second. By querying the cache directly, you can avoid the time-consuming and expensive process of querying the database, then mapping query results to cache lookups.
I ran across this yesterday in a web article with no hyperlinks and pointers only to other articles on itself. Honoring that degree of self-absorption by not mentioning it by name.
Another potential way to improve topic map engine performance.
There is a recent survey of Ehcache users that you may want to read.