Oh, is it now a built-in module in 9.4beta?

I've used it in 9.1 (downloading the patch, applying it, recompiling postgres..) - have found this article re: postgres caching mechanisms (and pg_prewarm use in particular (though re: pg_prewarm, most of it is about applying the patch itself, etc.)) useful:

http://raghavt.blogspot.com/2012/04/caching-in-postgresql.ht...

P.S. here are some more comments from the author: http://www.postgresql.org/message-id/CA+TgmoZihvzFW6n6pPwzDO... (btw, I've found the pgsql-hackers to be a great mailing list indeed!)