AW: AW: [Extern] Re: autovacuum on pg_catalog tables

I have some hundred (user) tables where only a small subset of them requires a more aggressive autovacuum.
Setting table level parameters on this small subset seems more straightforward to me.
Loosing this setting on pg_dump / pg_upgrade would be ok for me. Doesn't happen that often.

I tried this on postgres 9.6:

postgresql.conf -> allow_system_table_mods=on + pg_ctl restart

# alter table pg_catalog.pg_shdepend set (autovacuum_vacuum_scale_factor = 0, autovacuum_vacuum_threshold = 1000);
ERROR: shared tables cannot be toasted after initdb
Time: 0.618 ms
# alter table pg_catalog.pg_largeobject set (autovacuum_vacuum_scale_factor = 0, autovacuum_vacuum_threshold = 1000);
ERROR: AccessExclusiveLock required to add toast table.
Time: 0.590 ms
# alter table pg_catalog.pg_largeobject_metadata set (autovacuum_vacuum_scale_factor = 0, autovacuum_vacuum_threshold = 1000);
ERROR: AccessExclusiveLock required to add toast table.
Time: 1.601 ms

Any idea?

Thanks, Markus

Von: Zwettler Markus (OIZ) <Markus(dot)Zwettler(at)zuerich(dot)ch>
Gesendet: Freitag, 4. Juni 2021 17:44
An: Vijaykumar Jain <vijaykumarjain(dot)github(at)gmail(dot)com>
Cc: pgsql-general(at)lists(dot)postgresql(dot)org
Betreff: AW: [Extern] Re: autovacuum on pg_catalog tables

Thanks for the info.

I have a lot of LO manipulation and want a more aggressive autovacuum on some pg_catalog tables therefore.

I do not see any reason why this should not work or be at risk?

Markus

Von: Vijaykumar Jain <vijaykumarjain(dot)github(at)gmail(dot)com<mailto:vijaykumarjain(dot)github(at)gmail(dot)com>>
Gesendet: Freitag, 4. Juni 2021 17:37
An: Zwettler Markus (OIZ) <Markus(dot)Zwettler(at)zuerich(dot)ch<mailto:Markus(dot)Zwettler(at)zuerich(dot)ch>>
Cc: pgsql-general(at)lists(dot)postgresql(dot)org<mailto:pgsql-general(at)lists(dot)postgresql(dot)org>
Betreff: [Extern] Re: autovacuum on pg_catalog tables

ok, what i am sharing, DO NOT DO IT.
it is just to answer why it is not working :)
PostgreSQL: Documentation: 13: 19.17. Developer Options<https://www.postgresql.org/docs/current/runtime-config-developer.html>

postgres=# alter table pg_catalog.pg_largeobject_metadata set (AUTOVACUUM_VACUUM_COST_DELAY = 1);
ERROR: permission denied: "pg_largeobject_metadata" is a system catalog
postgres=# show allow_system_table_mods;
allow_system_table_mods
-------------------------
off
(1 row)

postgres=# set allow_system_table_mods TO 1;
SET
postgres=# show allow_system_table_mods;
allow_system_table_mods
-------------------------
on
(1 row)

postgres=# alter table pg_catalog.pg_largeobject_metadata set (AUTOVACUUM_VACUUM_COST_DELAY = 1);
ALTER TABLE

but you can always run vacuum manually on the table.
vacuum (verbose,analyze) pg_catalog.pg_largeobject_metadata;
INFO: vacuuming "pg_catalog.pg_largeobject_metadata"
INFO: index "pg_largeobject_metadata_oid_index" now contains 0 row versions in 1 pages
DETAIL: 0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO: "pg_largeobject_metadata": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL: 0 dead row versions cannot be removed yet, oldest xmin: 8083775
There were 0 unused item identifiers.
Skipped 0 pages due to buffer pins, 0 frozen pages.
0 pages are entirely empty.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO: analyzing "pg_catalog.pg_largeobject_metadata"
INFO: "pg_largeobject_metadata": scanned 0 of 0 pages, containing 0 live rows and 0 dead rows; 0 rows in sample, 0 estimated total rows
VACUUM

On Fri, 4 Jun 2021 at 20:10, Zwettler Markus (OIZ) <Markus(dot)Zwettler(at)zuerich(dot)ch<mailto:Markus(dot)Zwettler(at)zuerich(dot)ch>> wrote:
I would like to start a more aggressive autovacuum on pg_catalog tables like pg_largeobject.

So I tried as a superuser:

# alter table pg_catalog.pg_largeobject_metadata set (autovacuum_vacuum_scale_factor = 0, autovacuum_vacuum_threshold = 5000);
ERROR: permission denied: "pg_largeobject_metadata" is a system catalog

(How) Is it possible to change such table attributes on pg_catalog tables?

Thanks, Markus

--
Thanks,
Vijay
Mumbai, India

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