Re: autovacuum: I need some explanation - Mailing list pgsql-hackers

From Noah Freire
Subject Re: autovacuum: I need some explanation
Date
Msg-id d8dd025a0810291226v36babdccv79a3bbb4b5dd5d5c@mail.gmail.com
Whole thread Raw
In response to Re: autovacuum: I need some explanation  (Alvaro Herrera <alvherre@commandprompt.com>)
List pgsql-hackers

Hi Alvaro,

On Wed, Oct 29, 2008 at 3:46 PM, Alvaro Herrera <alvherre@commandprompt.com> wrote:
Noah Freire escribió:

> please check the first log message: the vacuum threshold is 6,000,050 rows
> and the number of dead tuples is 16,697,969. Even though the number of
> dead_tuples is greater than the threshold the autovacuum is not being
> triggered for this table. So, besides this condition (dead_tuples >
> threshold) what else is taken into account by autovacuum?

That there's no other process doing the same.  Did you check
pg_stat_activity to ensure that there's really no autovacuum worker
processing this table?
 
 datid | datname | procpid | usesysid | usename | current_query | waiting | xact_start | query_start | backend_start | client_addr | client_port
-------+---------+---------+----------+----------+-------------------------------------------------------------------------+---------+-------------------------------+-------------------------------+-------------------------------+-------------+-------------
 45974 | pgbench | 14660 | 10 | postgres | autovacuum: VACUUM public.accounts | f | 2008-10-29 11:09:05.610857-07 | 2008-10-29 11:09:05.610857-07 | 2008-10-29 11:09:03.45083-07 | |

indeed; autovacuum is currently running for accounts. It is running for 1 hour but the number of dead rows keeps increasing. Apparently autovacuum cannot pace the rate of updates on this table (please check the two snapshots of pg_stat_user_tables below taken with a 2 seconds interval between them). It would be better to run vacuum manually than using autovacuum in this case?
pgbench=# select relname, n_dead_tup from pg_stat_user_tables where relname='accounts';
 relname | n_dead_tup
----------+------------
 accounts | 19917490
(1 row)

pgbench=# select relname, n_dead_tup from pg_stat_user_tables where relname='accounts';
 relname | n_dead_tup
----------+------------
 accounts | 19923767
(1 row)

Thanks,
-Noah

pgsql-hackers by date:

Previous
From: Magnus Hagander
Date:
Subject: Re: minimal update
Next
From: Alvaro Herrera
Date:
Subject: Re: minimal update