[lispm]

One thing, of all the dynamic languages the default Ruby implementation is by far the slowest. For anything that is slighty computational expensive, the default Ruby implementation is poor. Also think green, if you have lots of computation in a slow language, that easily adds up in a large data center in form of wasted electricity, which adds to cooling and is generally expensive. Some Ruby implementations try to get in the direction of, say, a Lisp implementation like SBCL - which is used by ITA. SBCL provides since quite some time a compiler that can generate reasonably fast code.

[hga]

In Dan Weinreb's "Lisp for High-Performance Transaction Processing" talk he mentioned that SBCL was being used for QPX because of the quality of its compiled code (as I recall they started out with CMU CL so this was a natural choice).

For REs, Clozure CL was being used in part because faster compile times were more important and run time preformance was more than adequate; stateless business middleware is a very different beast than compute intensive route construction, where we can be sure the cutoff in optimizing choices is based on response time.

There were other reasons for Clozure CL, including the fact that it has a company behind it, one who's principles Dan and others have had long relationships with and ITA was buying one (man?)day a week of their services to support RES. SBCL is (has always been?) a volunteer effort.