Depends on the project. We have some that use PostgreSQL backed queues. Some using Redis. As you get more traffic RDBMS resources are precious - wasting them on queues starts to become a poor tradeoff. Redis is so generally useful we tend to use it on most projects anyways, so it doesn't add another moving part. And we tend to be really conservative about adding new things to our production environment, and despite that Redis has found a home in our stack.