Run update_subscription_facet_backend_data task in parallel
My upgrade is processing all hosts at rate of about 1-2 hosts per second, which gives quite long upgrade time for decently sized Satellite 6, I was on a host with thousand dummy hosts created. Server is baremetal ex-workstation and there is no load except rake, java and postgres (but it's not utilizing resources fully). It has 11k hosts with 125k of fact values.
We should run such rake tasks in parallel. It's not much work to run this in a threadpool or via channels, we already have ruby-concurrent gem. I'd expect huge speedup as this is mostly IO-bound operation (network, database).