Hi, On 2021-04-23 19:42:30 -0700, Peter Geoghegan wrote: > On Fri, Apr 23, 2021 at 7:33 PM Andres Freund <and...@anarazel.de> wrote: > > Check it every so often, independent of whether there are indexes or > > dead tuples? Or just check it at the boundaries. > > I think that the former suggestion might be better -- I actually > thought about doing it that way myself.
Cool. > The latter suggestion sounds like you're suggesting that we just check > it at the beginning and the end in all cases (we do the beginning in > all cases already, but now we'd also do the end outside of the loop in > all cases). Is that right? Yes. > If that is what you meant, then you should note that there'd hardly be > any check in the one-pass case with that scheme (apart from the > initial check that we do already). The only work we'd be skipping at > the end (in the event of that check triggering the failsafe) would be > heap truncation, which (as you've pointed out yourself) doesn't seem > particularly likely to matter. I mainly suggested it because to me the current seems hard to understand. I do think it'd be better to check more often. But checking depending on the amount of dead tuples at the right time doesn't strike me as a good idea - a lot of anti-wraparound vacuums will mainly be freezing tuples, rather than removing a lot of dead rows. Which makes it hard to understand when the failsafe kicks in. Greetings, Andres Freund
