During integration Till noticed that generating overviews was, slow. This was the slowest operation and the only one where the new Perl library fairs worse than the C so I am not surprised that it would come under inspection. Till tasked me with improving the performance. I was doubtful that improvements were possible, I was wrong. Once I profiled using NYTProf a clear bottleneck appeared, over half the run time was being spent cloning data structures. Many of these clones were unnecessary but resulted from me having removed the conditional cloning(I thought it made the code cleaner).
So that was my first experience with profiling. All together it went perfectly, even if only to uncover a bug of my own making.