I am running Apache 2.4.35 with event MPM. All MPM settings are at default values with the exception of MaxSpareThreads which is set to 100. This means, by default, ServerLimit = 16 and ThreadsPerChild = 25 which yields MaxRequestWorkers of 400.
After benching the server aggressively with AB, mod_status is showing 399 idle threads spread across 16 processes. This has been the case for a couple of days. Currently, the server is receiving zero traffic with the exception of manual tests via AB.
Can anyone explain why Apache is not killing processes to honor MaxSpareThreads? Screen capture of mod_status.