In short, I tend to agree with having one row per worker in the vacuum progress report, joining pg_stat_activity's leader_pid for simpler usability, extensibility, and less information bloat, along with doc changes to explain this. One concern is that some progress fields would be null on worker rows, but documenting this should be sufficient. I could be missing something here, so I would like to hear some thoughts before coming up with a patch.
I will look at the rest of the points later in detail, but it does sound like to me that a new worker view will be a better place to hold extra per worker ( or leader ) details and the current view will remain high level/progress data. Unused progress fields do not sound right to me, and I also worry we will bloat the existing view over time if we want to add more per worker fields.
