[jprosevear]

Solid Queue (by default actually) uses a second, segregated database for the queue. You can scale it independently of your app database.

[nickjj]

Yep but using 2 DBs within the same PG instance won't improve performance since it's using the same disk.

Managing multiple DB instances across multiple hosts requires a lot more effort, configuration and doubles your hosting costs vs running Redis on the same host with Sidekiq IMO.