Thread: pgsql: Add relallfrozen to pg_class
Add relallfrozen to pg_class Add relallfrozen, an estimate of the number of pages marked all-frozen in the visibility map. pg_class already has relallvisible, an estimate of the number of pages in the relation marked all-visible in the visibility map. This is used primarily for planning. relallfrozen, together with relallvisible, is useful for estimating the outstanding number of all-visible but not all-frozen pages in the relation for the purposes of scheduling manual VACUUMs and tuning vacuum freeze parameters. A future commit will use relallfrozen to trigger more frequent vacuums on insert-focused workloads with significant volume of frozen data. Bump catalog version Author: Melanie Plageman <melanieplageman@gmail.com> Reviewed-by: Nathan Bossart <nathandbossart@gmail.com> Reviewed-by: Robert Treat <rob@xzilla.net> Reviewed-by: Corey Huinker <corey.huinker@gmail.com> Reviewed-by: Greg Sabino Mullane <htamfids@gmail.com> Discussion: https://postgr.es/m/flat/CAAKRu_aj-P7YyBz_cPNwztz6ohP%2BvWis%3Diz3YcomkB3NpYA--w%40mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/99f8f3fbbc8f743290844e8c676d39dad11c5d5d Modified Files -------------- doc/src/sgml/catalogs.sgml | 20 ++++++ src/backend/access/heap/vacuumlazy.c | 18 ++++-- src/backend/catalog/heap.c | 2 + src/backend/catalog/index.c | 12 +++- src/backend/commands/analyze.c | 12 ++-- src/backend/commands/cluster.c | 5 ++ src/backend/commands/vacuum.c | 6 ++ src/backend/statistics/relation_stats.c | 29 +++++++-- src/backend/utils/cache/relcache.c | 2 + src/include/catalog/catversion.h | 2 +- src/include/catalog/pg_class.h | 3 + src/include/commands/vacuum.h | 1 + src/test/regress/expected/stats_import.out | 99 +++++++++++++++++++----------- src/test/regress/sql/stats_import.sql | 49 ++++++++++----- 14 files changed, 190 insertions(+), 70 deletions(-)
On 2025-Mar-03, Melanie Plageman wrote: > Add relallfrozen to pg_class > > Add relallfrozen, an estimate of the number of pages marked all-frozen > in the visibility map. > > pg_class already has relallvisible, an estimate of the number of pages > in the relation marked all-visible in the visibility map. This is used > primarily for planning. > > relallfrozen, together with relallvisible, is useful for estimating the > outstanding number of all-visible but not all-frozen pages in the > relation for the purposes of scheduling manual VACUUMs and tuning vacuum > freeze parameters. I'm confused about this. Why was the new value added to pg_class instead of to the pgstat system? I don't think relallvisible is a good precedent, because as you write here, that one is used for planning, which has different requirements. For vacuuming metrics we rely on pgstat. -- Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/ "El número de instalaciones de UNIX se ha elevado a 10, y se espera que este número aumente" (UPM, 1972)
On Mon, Mar 3, 2025 at 11:44 AM Álvaro Herrera <alvherre@alvh.no-ip.org> wrote: > > On 2025-Mar-03, Melanie Plageman wrote: > > > relallfrozen, together with relallvisible, is useful for estimating the > > outstanding number of all-visible but not all-frozen pages in the > > relation for the purposes of scheduling manual VACUUMs and tuning vacuum > > freeze parameters. > > I'm confused about this. Why was the new value added to pg_class > instead of to the pgstat system? I don't think relallvisible is a good > precedent, because as you write here, that one is used for planning, > which has different requirements. For vacuuming metrics we rely on > pgstat. We use relpages and reltuples from pg_class in relation_needs_vacanalyze() in the same way relallfrozen is being used here. If we don't want relallfrozen in pg_class then there is no reason we wouldn't also move relallvisible out of pg_class too. - Melanie
Hi, On 2025-03-03 17:44:54 +0100, Álvaro Herrera wrote: > On 2025-Mar-03, Melanie Plageman wrote: > > > Add relallfrozen to pg_class > > > > Add relallfrozen, an estimate of the number of pages marked all-frozen > > in the visibility map. > > > > pg_class already has relallvisible, an estimate of the number of pages > > in the relation marked all-visible in the visibility map. This is used > > primarily for planning. > > > > relallfrozen, together with relallvisible, is useful for estimating the > > outstanding number of all-visible but not all-frozen pages in the > > relation for the purposes of scheduling manual VACUUMs and tuning vacuum > > freeze parameters. > > I'm confused about this. Why was the new value added to pg_class > instead of to the pgstat system? I don't think relallvisible is a good > precedent, because as you write here, that one is used for planning, > which has different requirements. For vacuuming metrics we rely on > pgstat. We do so because updating the other stats would cause too much churn - the number of dead tuples etc changes rather rapidly. That's not the case here. Having reliable information after a crash (where we loose pgstats) that 95% of the table is actually frozen, rather than not seems good. Greetings, Andres Freund
On Mon, Mar 3, 2025 at 11:48 AM Melanie Plageman <melanieplageman@gmail.com> wrote: > > On Mon, Mar 3, 2025 at 11:44 AM Álvaro Herrera <alvherre@alvh.no-ip.org> wrote: > > > > I'm confused about this. Why was the new value added to pg_class > > instead of to the pgstat system? I don't think relallvisible is a good > > precedent, because as you write here, that one is used for planning, > > which has different requirements. For vacuuming metrics we rely on > > pgstat. > > We use relpages and reltuples from pg_class in > relation_needs_vacanalyze() in the same way relallfrozen is being used > here. Sorry reltuples only (not relpages). - Melanie