On Mon, 28 Aug 2023 at 17:14, Robert Haas <robertmh...@gmail.com> wrote: > > On Mon, Aug 28, 2023 at 10:52 AM Matthias van de Meent > <boekewurm+postg...@gmail.com> wrote: > > In this new patch, I've updated a few comments to get mostly within > > line length limits; the name of the storage parameter is now > > "local_update_limit", as per discussion on naming. > > I've also added local_update_limit to psql's autocomplete file, and > > added documentation on how the parameter behaves - including warnings > > - in create_table.sgml. > > I feel like this is the sort of setting that experts will sometimes be > able to use to improve the situation, and non-experts will have great > difficulty using. It relies on the user to know what size limit will > work out well, which probably involves knowing how much real data is > in the table, and how that's going to change over time, and probably > also some things about how PostgreSQL does space management > internally. I don't know that I'd be able to guide a non-expert user > in how to make effective use of this as a tool.
Agreed on all points. But isn't that true for most most tools on bloat prevention and/or detection? E.g. fillfactor, autovacuum_*, ... > I don't know exactly what to propose, but I would definitely like it > if we could come up with something with which a casual user would be > less likely to shoot themselves in the foot and more likely to derive > a benefit. I'd prefer that too, but by lack of other work in this area this seems like it fills a niche that would otherwise require extremely expensive locking over a long time for CLUSTER, superuser+pg_repack, or manual scripts that update tuples until they're located on a different page (begin; update tuple WHERE ctid > '(12,0)' returning ctid; ...; commit;). I agree this is very minimal and can definitely be used as a footgun, but with the description that it can be a footgun I don't think it's (much) worse than the current situation - a user should only reach for this once they've realized they actually have an issue. Kind regards, Matthias van de Meent Neon (https://neon.tech)
