So far as I know, Rally using async HTTP request to bulk index docs. And the implementation is in driver.py
I could perform similar requests using REST client. Consedering that asynchronised request does not wait response from ES server and REST client could send another requet. So, this cause a problem that ES server could not handle so many index requests in a quite short period.
I'm wondering to know, how often does Rally send requests to ES server? How does it calculate the period.