I'm hacking on some tools that use the Search::Xapian module to build up search indexes. It's an excellent Perl interface to Xapian, but unfortunately it seemed to be too slow for our purposes. Tracing our code showed that much of the slowness was in passing data back and forth between Perl and the C++ library for every call.
I decided to write my own XS module to speed things up. Instead of using Search::Xapian, I'd bundle everything up into a Perl datastructure, and pass it down to libxapian through my own module, once, and do all the indexing work in C++. This worked great -- until I started trying to do some exception handling.