On Wed, 6 Mar 2024 at 11:33, Stephen Frost <sfr...@snowman.net> wrote: > On Wed, Mar 6, 2024 at 11:07 Matthias van de Meent > <boekewurm+postg...@gmail.com> wrote: >> Or even just one VALUES for the whole statistics loading? > > > I don’t think we’d want to go beyond one relation at a time as then it can be > parallelized, we won’t be trying to lock a whole bunch of objects at once, > and any failures would only impact that one relation’s stats load.
That also makes sense. >> I suspect the main issue with combining this into one statement >> (transaction) is that failure to load one column's statistics implies >> you'll have to redo all the other statistics (or fail to load the >> statistics at all), which may be problematic at the scale of thousands >> of relations with tens of columns each. > > > I’m pretty skeptical that “stats fail to load and lead to a failed > transaction” is a likely scenario that we have to spend a lot of effort on. Agreed on the "don't have to spend a lot of time on it", but I'm not so sure on the "unlikely" part while the autovacuum deamon is involved, specifically for non-upgrade pg_restore. I imagine (haven't checked) that autoanalyze is disabled during pg_upgrade, but pg_restore doesn't do that, while it would have to be able to restore statistics of a table if it is included in the dump (and the version matches). > What are the cases where we would be seeing stats reloads failing where it > would make sense to re-try on a subset of columns, or just generally, if we > know that the pg_dump version matches the target server version? Last time I checked, pg_restore's default is to load data on a row-by-row basis without --single-transaction or --exit-on-error. Of course, pg_upgrade uses it's own set of flags, but if a user is restoring stats with pg_restore, I suspect they'd rather have some column's stats loaded than no stats at all; so I would assume this requires one separate pg_import_pg_statistic()-transaction for every column. Kind regards, Matthias van de Meent Neon (https://neon.tech)
