On Wednesday, July 27, 2011, Maxim Dounin <mdounin@mdounin.ru> wrote:

> Keepalive connections are mostly beneficial if response costs are
> comparable with connection establishment costs (i.e. over
> high-latency links or with really fast backends).

There's an additional benefit for high-traffic reverse proxy installations (for example, sites that use nginx as a load balancer) : with keepalive connections, there's less risk of running out of ephemeral port numbers - or less need to decrease the TIME_WAIT interval to free up ephemeral port numbers faster.