In postgres, when autovacuum runs and for some reason say its able to perform autovacuum - for example when hot_standby_feedback is set and there are long running queries on standby. Say for example tab1 has been updated and it triggers autovacuum, meanwhile a long running query on standby is running and sends this info to primary which will skip the vacuum on tab1.
Since the autovacuum got skipped for tab1, When does autovacuum run vacuum on the table again? Or it will not run autovacuum again on it and we would need to manually run vacuum on that table. Basically does autovacuum retry autovacuum on tables that could not be vacuumed for the first time?
Autovacuum does not get skipped due to hot_standby_feedback. It still runs, it just might not accomplish anything if no rows can be removed. If this is the case, then pg_stat_all_tables.n_dead_tup does not get decremented, which means that the table will probably get autovacuumed again the next time the database is assessed for autovacuuming as the stats that make it eligible have not changed. On an otherwise idle system, this will happen about once every however long it takes to scan not-all-visible part of the table, rounded up to the next increment of autovacuum_naptime.
It might be a good idea (although the use case is narrow enough that I doubt it) to suppress repeat autovacuuming of a table until the horizon has advanced far enough to make it worthwhile, but currently there is no code to do this.
Note that this differs from INSERT driven autovacuums. There, n_ins_since_vacuum does get reset, even if none of the tuples were marked all visible. So that vacuum will not get run again until the table cross some other threshold to make it eligible.
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I have a scenario that repeats itself every few hours. In every few hours, there is a sudden increase in row exclusive locks in PostgreSQL DB. In Meantime there seems that some queries are not responded in time and causes connection exhaustion to happen that PostgreSQL does not accept new clients anymore. After 2-3 minutes locks and connection numbers drops and the system comes back to normal state again.
I wonder if auto vacuum can be the root cause of this? I see analyze and vacuum (NOT FULL VACCUM) take about 20 seconds to complete on one of the tables. I have INSERT,SELECT,UPDATE and DELETE operations going on from my application and I don't have DDL commands (ALTER TABLE, DROP TABLE, CREATE INDEX, ...) going on. Can auto vacuum procedure conflict with queries from my application and cause them to wait until vacuum has completed? Or it's all the applications and my bad design fault? I should say one of my tables has a field of type jsonb that keeps relatively large data for each row (10 MB roughly).
I have attached an image from monitoring application that shows the sudden increase in row exclusive locks.
ROW EXCLUSIVE locks are perfectly harmless; they are taken on tables against which DML statements run. Your graph reveals nothing. You should set log_lock_waits = on and log_min_duration_statement to a reasonable value. Perhaps you can spot something in the logs. Also, watch out for long running transactions.
We're having some issues when autovacuum triggers on one of our large tables (~100Gb).
Our ETL jobs only hit the last three partition of this table but, from my understanding, when autovacuum is triggered on a partition the whole table is vacuumed and this is causing the ETL job to wait until it's finished.
So far I've tried to set autovacuum_vacuum_scale_factor to both a higher and lower value which yields approximately the same execution time for our job.
Since a rather important number of INSERT/UPDATE is performed on this table, I would like to put a low value for autovacuum_vacuum_scale_factor on the three lasts partitions, but prevent the vacuuming of older partitions.
We are already using a vacuum script that runs every evening so I'm thinking about setting autovacuum_enabled to off on older partitionned and let the script handle the vacuum on these tables, but I'm not sure if it's the right way to treat this problem.
Another parameter I've stumbled upon is the vacuum_freeze_min_age and autovacuum_freeze_max_age, but I'm not sure I understand how to use them.
Team,
Recently identified one of the table autovacuum was in up to date but autoanalyze is not up to date. Parameters are configured default.
How this will happen? If autovacuum parameters satisfied the conditions then it should have performed autoanalyze as well .
Please share some insights on this.
Thanks
Autovacuum and autoanalyze are triggered by different conditions and use different statistics counters:
autovacuum starts running if the number of dead tuples (n_dead_tup in pg_stat_all_tables) exceeds a threshold (by default, about 20% of reltuples from pg_class). From v13 on, there is a similar condition with n_ins_since_vacuum, the number of tuples inserted since the last VACUUM.
autoanalyze starts running if the number of changed tuples (n_mod_since_analyze in pg_stat_all_tables) exceeds a threshold (by default, about 10% of reltuples from pg_class).
Whenever autovacuum or autoanalyze have completed, the respective statistics counter is reset to 0.
So there is no direct connection between autovacuum and autoanalyze runs (except that both are connected to table modifications, unless it is an anti-wraparound vacuum run).
Postgresql has the functionality of Vacuum for recollecting the space occupied by dead tuples. Auto vacuum is on by default and runs according to the configuration setting.
When I check the output of pg_stat_all_tables i.e. last_vacuum and last_autovacuum, autovacuum was never run for most of the tables in the database which have enough number of dead tuples(more than 1K). We also get a time window of 2-3 hours when these tables are used rarely.
Below are autovacuum settings for my database
below is the output of pg_stat_all_tables
I want to ask that is it a good idea to depend only on auto vacuum?
Are there any special setting required for autovacuum to function properly?
Should we set up a manual vacuum? Should we use both in parallel or just turn off autovacuum and use manual vacuum only?
You should definitely use autovacuum.
Are there any autovacuum processes running currently?
Does a manual VACUUM on such a table succeed?
Set log_autovacuum_min_duration = 0 to get information about autovacuum processing in the logs.
If system activity is too high, autovacuum may not be able to keep up. In this case it is advisable to configure autovacuum to be more aggressive, e.g. by setting autovacuum_vacuum_cost_limit = 1000.
https://www.postgresql.org/docs/current/static/routine-vacuuming.html
PostgreSQL databases require periodic maintenance known as vacuuming.
For many installations, it is sufficient to let vacuuming be performed
by the autovacuum daemon, which is described in Section 24.1.6. You
might need to adjust the autovacuuming parameters described there to
obtain best results for your situation. Some database administrators
will want to supplement or replace the daemon's activities with
manually-managed VACUUM commands, which typically are executed
according to a schedule by cron or Task Scheduler scripts.
vacuum creates significant IO, asjust https://www.postgresql.org/docs/current/static/runtime-config-resource.html#RUNTIME-CONFIG-RESOURCE-VACUUM-COST to fit your needs.
Also you can set autovacuum settings per table, to be more "custom" https://www.postgresql.org/docs/current/static/sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS
the above will give you the idea why your 1K dead tuples might be not enough for autovacuum and how to change it.
manual VACUUM is a perfect solution for one time run, while to run the system I'd definitely rely on autovacuum daemon
I'm working an part of a system where tables need to be locked in "IN SHARE ROW EXCLUSIVE MODE NOWAIT" mode.
The problem is that the Autovacumn daemon (autovacuum: ANALYZE) kicks in immediately on a table after it has been worked on - stopping the next process from taking a "IN SHARE ROW EXCLUSIVE MODE NOWAIT".
The tables are large so the vacuum takes a while. I could check for this before the transaction that is trying to lock starts and use pg_cancel_backend to stop the autovacuum daemon. Are there any consequences to this? The other option is to manually schedule vacuuming but everywhere you read it's best to avoid this. Are there any parameters which I have missed that could tweak the autovacuum to stop it from behaving like this?
Thanks
If you keep autovacuum from working, you will incur table bloat and eventually risk downtime when PostgreSQL shuts down to avoid data loss due to transaction ID wraparound.
Disabling autovacuum for this table (ALTER TABLE ... SET (autovacuum_enabled = off)) and regularly scheduling a manual VACUUM is an option.
But it would be best to change your procedure so that you don't have to lock tables explicitly all the time.