On Tue, Mar 2, 2021 at 6:44 PM Masahiko Sawada <sawada.m...@gmail.com> wrote: > A scale type parameter seems good to me but I wonder if how users can > tune that parameter. We already have tuple-based parameters such as > autovacuum_vacuum_scale_factor/threshold and I think that users > basically don't pay attention to that table updates result in how many > blocks.
Fair. The scale thing was just a random suggestion, nothing to take too seriously. > The third idea is a VACUUM command option like DISABLE_PAGE_SKIPPING > to disable such skipping behavior. I imagine that the > user-controllable-option to enforce both heap vacuum and index vacuum > would be required also in the future when we have the vacuum strategy > feature (i.g., incremental vacuum). Yeah, I'm worried about conflicting requirements here -- this patch and the next patch (that pushes the same ideas further) might have different requirements. I think that this patch will mostly be useful in cases where there are very few LP_DEAD-containing heap pages, but consistently more than zero. So it's probably not easy to tune. What we might want is an on/off switch. But why? DISABLE_PAGE_SKIPPING was added because the freeze map work in 9.6 was considered high risk at the time, and we needed to have a tool to manage that risk. But this patch doesn't seem nearly as tricky. No? > > Lots of stuff in this area is kind of weird already. Sometimes this is > > directly exposed to users, even. This came up recently, when I was > > working on VACUUM VERBOSE stuff. > That's true. I didn't know that. It occurs to me that "tups_vacuumed vs. total LP_DEAD Items in heap after VACUUM finishes" is similar to "pages_newly_deleted vs. pages_deleted" for indexes. An easy mistake to make! > > https://www.postgresql.org/message-id/flat/20130108024957.GA4751%40tornado.leadboat.com > > > > Of course, this effort to eliminate the "tupgone = > > true"/XLOG_HEAP2_CLEANUP_INFO special case didn't go anywhere at the > > time. > > I'll look at that thread. I'm not sure if it's super valuable to look at the thread. But it is reassuring to see that Noah shared the intuition that the "tupgone = true" case was kind of bad, even back in 2013. It's one part of my "mental map" of VACUUM. -- Peter Geoghegan
