Hi, On 2022-03-24 21:06:21 -0700, Peter Geoghegan wrote: > On Thu, Mar 24, 2022 at 8:56 PM Thomas Munro <thomas.mu...@gmail.com> wrote: > > Interesting. IIUC your chaos gizmo shows that particular vacuum test > > still failing on master, but that wouldn't happen in real life because > > since 383f2221 it's a temp table. Your gizmo should probably detect > > temp rels, as your comment says. I was sort of thinking that perhaps > > if DISABLE_PAGE_SKIPPING is eventually made to do what its name sounds > > like it does, we could remove TEMP from that test and it'd still pass > > with the gizmo... > > Why not just use VACUUM FREEZE? That should work, because it won't > settle for a cleanup lock on any page with an XID < OldestXmin. And > even if there were only LP_DEAD items on a page, that wouldn't matter > either, because we don't need a cleanup lock to get rid of those > anymore. And we consistently do all the same steps for rel truncation > in the no-cleanup-lock path (lazy_scan_noprune) now. > > I think that DISABLE_PAGE_SKIPPING isn't appropriate for this kind of > thing. It mostly just makes VACUUM not trust the visibility map, which > isn't going to help. While DISABLE_PAGE_SKIPPING also forces > aggressive mode, that isn't going to help either, unless you somehow > also make sure that FreezeLimit is OldestXmin (e.g. by setting > vacuum_freeze_min_age to 0). > > VACUUM FREEZE (without DISABLE_PAGE_SKIPPING) seems like it would do > everything you want, without using a temp table. At least on the > master branch.
We tried that in a prior case: https://postgr.es/m/20220120052404.sonrhq3f3qgplpzj%40alap3.anarazel.de I don't know if the same danger applies here though. Greetings, Andres Freund
