> long-timeout HTTP connection that wouldn't be responded to This open connection IS the overhead. Some approaches have more overhead, some less. Long-polling

> long-timeout HTTP connection that wouldn't be responded to This open connection IS the overhead. Some approaches have more overhead, some less. Long-polling these days is not needed and can be replaced by SSE [1] (if you are OK with unidirectional communication), websockets (bidirectional), or callback URIs in the request. The latter is a per-request webhook, essentially, and would have the lowest overhead at the cost of ceremony (the client now needs to have a running web server). By the way, long polling was popularized by Comet [2] around 2006. [1]: https://en.wikipedia.org/wiki/Server-sent_events https://en.wikipedia.org/wiki/Server-sent_events [2]: https://en.wikipedia.org/wiki/Comet_(programming) https://en.wikipedia.org/wiki/Comet_(programming)