Your CTO is right. I was recently in the position of using Tokyo Cabinet on a site with a lot of traffic. Initially, it was great. It continued to be great for a long while until we hit a point where it started taking up too much memory and 100% cpu causing load to sky rocket. While the technology is great, there was very little that Google found about our particular problem. We eventually wound up resetting our tyrant database and plan on moving completely off of it.