On Fri, Feb 07, 2025 at 02:21:07PM -0500, Melanie Plageman wrote: > On Fri, Feb 7, 2025 at 12:37 PM Nathan Bossart <nathandboss...@gmail.com> > wrote: >> My first reaction is to question whether >> it makes send to have two strategies for this sort of thing: >> autovacuum_vacuum_max_threshold for updates/deletes and this for inserts. >> Perhaps we don't want to more aggressively clean up bloat (except for the >> very largest tables via the hard cap), but we do want to more aggressively >> mark newly-inserted tuples frozen. I'm curious what you think. > > The goal with insert-only tables is to set the whole page frozen in > the VM. So, the number of pages is more important than the total > number of tuples inserted. Whereas, with updates/deletes, it seems > like the total amount of garbage (# tuples) needing cleaning is more > important.
I think this is a reasonable position. To be clear, I don't have a problem with having different strategies, or even with swapping autovacuum_vacuum_max_threshold with a similar change, if it's the right thing to do. I just want to be able to articulate why they're different. >> Wouldn't relallvisible be sufficient here? We'll skip all-visible pages >> unless this is an anti-wraparound vacuum, at which point I would think the >> insert threshold goes out the window. > > It's a great question. There are a couple reasons why I don't think so. > > I think this might lead to triggering vacuums too often for > insert-mostly tables. For those tables, the pages that are not > all-visible will largely be just those with data that is new since the > last vacuum. And if we trigger vacuums based off of the % not > all-visible, we might decrease the number of cases where we are able > to vacuum inserted data and freeze it the first time it is vacuumed -- > thereby increasing the total amount of work. Rephrasing to make sure I understand correctly: you're saying that using all-frozen would trigger less frequent insert vacuums, which would give us a better chance of freezing more than more frequent insert vacuums triggered via all-visible? My suspicion is that the difference would tend to be quite subtle in practice, but I have no concrete evidence to back that up. -- nathan
