"It was probably faster to read ssh keys from MySQL than their file-system. Apparently Engine Yard is using GFS which, according to what I've read, tend to be slow. When you have 1000+ keys it is probably faster to read it from a MySQL server which doesn't have the GFS bottleneck. But that's a rather special case. It illustrates well how little things can have a dramatic impact when you 'scale'. This kind of optimization might be useless or even harmless in other situations; but their particular problem it was worth it." - Henry Prêcheur