If your developers don’t know how to squeeze performance out of your server then they should either be taught how or shown.
Tune the performance of Grails apps
For many developers, a standard Grails application works plenty fast enough, particularly with judicious use of caching. Yet there is almost always a trade-off between convenience and flat out speed. So if you need to increase the number of concurrent users that can be handled or increase the number of requests per second that are processed, read on.
But! Before you do, please remember that every application is different. Sometimes an application is slow simply because it’s executing way more queries than it needs to. For that reason, you should always profile your application to find out what’s happening. The following suggestions only really apply if you discover that it’s not your application code that’s the problem.
via How To: Tune the performance of Grails apps.