Redis is fundamentally the wrong storage system for a job queue when you have an RDBMS handy. This is not new information. You still might want to split the job queue onto its own DB server when things start getting busy, though.

For caching, though, I wouldn’t drop Redis so fast. As a in-memory cache, the ops overhead of running Redis is a lot lower. You can even ignore HA for most use cases.

Source: I helped design and run a multi-tiered Redis caching architecture for a Rails-based SaaS serving millions of daily users, coordinating shared data across hundreds of database clusters and thousands of app servers across a dozen AWS regions, with separate per-host, per-cluster, per-region, and global cache layers.

We used Postgres for the job queues, though. Entirely separate from the primary app DBs.