[KraftyOne]

The key is that the UDF's enqueue is transactional with the database update. Let's say the database update is inserting a new order. This provides the guarantee that if a new order is inserted, a job to process the order is also enqueued. It's impossible for a new order to be inserted without its processing job also being enqueued. Then the durable workflow/queue system is responsible for making sure the processing job, once enqueued, actually executes.

[LgWoodenBadger]

And if that job never runs? Or if that job runs and then fails to commit that it ran in postgres?

[halfcat]

The job will run the next time a worker runs (in both cases).

And doesn’t that mean the job potentially runs twice? Yes.

In DBOS there are two kinds of “things that run”: workflows, and steps (workflows are made of steps).

Workflows must be deterministic (so it’s fine if it runs twice). Steps don’t have to be deterministic but have at-least-once execution (so it’s best if these are idempotent).