I'm missing the connection between poor API performance under Rails and the decision to do a ground-up rewrite. Was the initial performance problem due to an API problem or a platform problem? Was there any profiling of the poorly performing API server? I'd love to hear the story behind that analysis and how it impacted the tale told in TFA.

I ask all this since I've lost count of how many times I've participated in or witnessed an averted rewrite via a good dose of profiling and a few key bugfixes. I'll acknowledge that's not as fun as a clean-slate project, but vast amounts of engineering time were saved.