On Fri, Aug 20, 2021 at 12:20 PM Robert Haas <robertmh...@gmail.com> wrote: > On Fri, Aug 20, 2021 at 3:13 PM Peter Geoghegan <p...@bowt.ie> wrote: > > In short: yeah, this "closed vs open" page business more or less > > necessitates tightening things up here. Though this new requirement > > seems to have always been a good idea. Just because we can lean on > > VACUUM like this (an option that other DB systems don't have) doesn't > > mean that we should do so. > > That's all true, but it's not what I was talking about.
Then I am not sure that I have understood you fully. I would like to make sure that I have the nuance of it. As long as we have the idea of open vs closed pages then we cannot assume that we know that status from the page alone. Unless we're willing to go update the pages again, and possibly dirty them again, which seems unappealing. My concern here is really the data structure and its overall complexity. If there has to be an explicit state for every page on the FSM, then this new FSM needs to merge freelists that have been emptied into that structure, and needs to handle the question of which structure (map or free lists) is currently authoritative for a given heap page. That's a lot of complexity compared to just forgetting the free lists that are known to be fully closed, which will probably be very common. That can work a little like discarding old UNDO -- it can be simple and cheap *because* it's largely logical and implicit at the level of the physical data structures. -- Peter Geoghegan
