open), and catch the exception raised for nonexistent files. This is generally a poor choice performance-wise on JRuby, but is also not necessarily ideal on MRI.
ActiveRecord maintains a pool of database connections that may be used by multiple threads to perform database work. If many threads are contending for a smaller number of connections, the behavior of the connection pool becomes important.
Rack is an interface for Ruby components accepting and responding to HTTP requests synchronously. Though there is not an official Rack spec for asynchronous responses, Rack servers such as Rainbows! and Thin provide an asynchronous interface for responses that may happen at an unknown time in the future, such as in a web chat room.