Chapter "The True Cost of Redis" surprised me.

> Deploy, version, patch, and monitor the server software

And with PostgreSQL you don't need it?

> Configure a persistence strategy. Do you choose RDB snapshots, AOF logs, or both?

It's a one-time decision. You don't need to do it daily.

> Sustain network connectivity, including firewall rules, between Rails and Redis

And for a PostgreSQL DB you don't need it?

> Authenticate your Redis clients

And your PostgreSQL works without that?

> Build and care for a high availability (HA) Redis cluster

If you want a cluster of PostgreSQL databases, perhaps you will do that too.

I guess the point is that you're already doing it for postgres. You alrrady need persistent storage for your app, and the same engine can handle your queuing needs.