To improve performance and conserve network bandwidth, the T4 API will cache historical chart data to a local cache file. T4 API manages the cache file automatically and has a maximum size limit in place for it. Additionally, if you make multiple requests for chart data rapidly then these will be queued and processed one at a time. It should also be noted that chart data responses can be raised on different threads and be raised at the same time as other events from within the API and that the order of responses may not match the order the requests were made in.