Idk about pgagent but any table is a resilient queue with the multiple locks available in pg along with some SELECT pg_advisory_lock or SELECT FOR UPDATE queries, and/or LISTEN/NOTIFY.

Several bg job libs are built around native locking functionality

> Relies upon Postgres integrity, session-level Advisory Locks to provide run-once safety and stay within the limits of schema.rb, and LISTEN/NOTIFY to reduce queuing latency.

https://github.com/bensheldon/good_job

> |> lock("FOR UPDATE SKIP LOCKED")

https://github.com/sorentwo/oban/blob/8acfe4dcfb3e55bbf233aa...

i think the parent commenter has confused "without any extensions" and "without installing any more extensions than the ones i've already installed"