> graphile-worker is horizontally scalable. Each instance has a customisable worker pool, this pool defaults to size 1 (only one job at a time on this worker) but depending on the nature of your tasks (i.e. assuming they're not compute-heavy) you will likely want to set this higher to benefit from Node.js' concurrency.
Regarding the horizontal scalability; that relates to if you have heavy tasks (tasks that take a second or more to execute) - you can use more instances to get higher throughput.
Hope this helps!