Someone mentioned about dramatiq-pg (https://gitlab.com/dalibo/dramatiq-pg) which also uses PG as the task queue backend and jsonb for message payload & result. How similar is that comparing to Oban?

I don't know about the technical differences, but having used dramatiq in production for 3 years now I can say it's 100% awesome, it's been rock solid for us handling many thousands of tasks daily.

I love PG but would never use it for message queueing. Postgres needs periodic table maintenance, autovacuum tuning for tables with high number of writes, and IMO can never be as good as RabbitMQ for distributed task queues. RabbitMQ is purpose built around messages and it's extremely reliable and performant.