For something like this, I would instinctively reach for an external queue mechanism instead of trying to work through the complexity of golangs concurrency.

Create a bunch of sequentially numbered jobs that then update their output into postgres database. Then have N number of workers process the jobs. Something like GCP's CloudTasks is perfect for this because the "workers" are just GCP Cloud Functions, so you can have a near infinite number of them (limited by concurrent DB connections).

This approach also buys you durability of the queue for free (ie: what happens when you need to stop your golang process mid queue?).

Then it is just a query:

  select * from finished_jobs order by job_num;