On Wed, Jan 25, 2023 at 10:56 PM Andres Freund <and...@anarazel.de> wrote: > but that's only true because page level freezing neutered > vacuum_freeze_min_age. Compared to <16, it's a *huge* change.
Do you think that page-level freezing (1de58df4fec7325d91f5a8345757314be7ac05da) was improvidently committed? I have always been a bit skeptical of vacuum_freeze_min_age as a mechanism. It's certainly true that it is a waste of energy to freeze tuples that will soon be removed anyway, but on the other hand, repeatedly dirtying the same page for various different freezing and visibility related reasons *really sucks*, and even repeatedly reading the page because we kept deciding not to do anything yet isn't great. It seems possible that the page-level freezing mechanism could help with that quite a bit, and I think that the heuristic that patch proposes is basically reasonable: if there's at least one tuple on the page that is old enough to justify freezing, it doesn't seem like a bad bet to freeze all the others that can be frozen at the same time, at least if it means that we can mark the page all-visible or all-frozen. If it doesn't, then I'm not so sure; maybe we're best off deferring as much work as possible to a time when we *can* mark the page all-visible or all-frozen. In short, I think that neutering vacuum_freeze_min_age at least to some degree might be a good thing, but that's not to say that I'm altogether confident in that patch, either. -- Robert Haas EDB: http://www.enterprisedb.com
