Store last created model's row in memory
You'd either have to use a cache, or fetch the most recent change on each request (since you can't persist objects between requests in-memory).
From what you describe, it sounds as if it's being hit fairly frequently, so the cache is probably the way to go.
I am working on ajax-game. The abstract: 2+ gamers(browsers) change a variable which is saved to DB through json. All gamers are synchronized by javascript-timer+json - periodically reading that variable from DB. 
In general, all changes are stored in DB as history, but I want the recent change duplicated in memory. 
So the problem is: i want one variable to be stored in memory instead of DB.