The thread and file-descriptor usage by each client was
Client threads fd-nr -------------------------------------------------- boost-redis-corosio 3 7 boost-redis-asio-co 2 7 boost-redis-asio-cb 2 7 redis-rs 1 10 go-redis 24 1006
I wonder why Corosio has one more thread than the ASIO variants. Does Corosio start an internal thread for some purpose? I'm assuming, the client code was equivalent for each library, or at least for the different variants of Boost.Redis.
Also, worth noting that, according to the GitHub page you referenced, the number of context switches were the highest for Corosio, and the amount of system time was a bit higher than ASIO. This may be related to the additional thread being used.
The extra thread is allocated by the timer service in Capy, underlying capy::delay() and capy::timeout(). Capy doesn't know about Corosio, so I don't think it can use io_context threads to run timers.