For anyone curious, we've been working to reduce the memory overhead and have added some stats to keep track of memory usage over time. On this graph, you can see a comparison with the CRuby interpreter:
Yes. Prior to that point we used to allocate a large chunk of executable memory upfront. We switched to mapping that memory on demand, and that alone was a huge improvement.
That is huge, did it also reduce(~~bring in~~) tail latency?
*edit, fix confusing vernacular
Nope -- P99 also decreased. I've heard similar things for other Rails apps as well.
Sorry, in my usage "bring in" means move tail latency P99/P100 more to the left not as introduce, I'll be more clear next time.