> Never use your primary DB as a queue. Using a separate Postgres instance can work if you over-provision capacity and don't need to maximize throughput, and a Redis-based solution can work if you don't need high availability and can tolerate some messages lost if something goes wrong.
That is a broad generalization that assumes most applications are operating at mega scale. The benefits of simplified dependencies (a single database instance), transactional guarantees (a single database instance) and persistence (not using Redis) far outweigh the eventual possibility that the queue will place too large a load on your database.
As the author of Oban[0] (an PG backed persistent queue in Elixir) I'm definitely biased. However, the level of adoption in the Elixir community seems to signal that a lot of companies favor simplicity and safety over a possible scale issue down the road. The primary application I work on processes ~500k-1m jobs a day and the queue overhead is virtually invisible.