Re: autovacuum ignores some tables

2011/6/23 Gábor Farkas <gabor(at)nekomancer(dot)net>:
> 2011/6/23 Thom Brown <thom(at)linux(dot)com>:
>> 2011/6/23 Gábor Farkas <gabor(at)nekomancer(dot)net>:
>>> hi,
>>>
>>> postgresql8.4.7 here.
>>>
>>> i checked the pg_stat_user_tables table, and it have a lot of rows
>>> there where the "last_autovacuum" and/or "last_autoanalyze" are null.
>>> does this mean that autovacuum never worked on those tables?
>>>
>>> roughly 70% of all the tables have null in those fields..
>>> in those never-autovacuumed tables there are tables that are quite
>>> big, and also have a lot of activity, so it's not that they never
>>> needed vacuuming...
>>>
>>> i wonder why autovacuum ignored them. i checked my settings with "SHOW
>>> ALL" in psql, and the corresponding settings are:
>>>
>>> autovacuum                       on
>>> autovacuum_analyze_scale_factor  0.1
>>> autovacuum_analyze_threshold     50
>>> autovacuum_freeze_max_age        200000000
>>> autovacuum_max_workers           3
>>> autovacuum_naptime               1min
>>> autovacuum_vacuum_cost_delay     20ms
>>> autovacuum_vacuum_cost_limit     -1
>>> autovacuum_vacuum_scale_factor   0.2
>>> autovacuum_vacuum_threshold      50
>>> track_counts on
>>>
>>> any ideas why autovacuum ignores some of the tables?
>>
>> The table may have not had enough updates or deletes to trigger a
>> vacuum.  Are these insert-only tables?  When you look at
>> pg_stat_user_tables, check the n_tup_upd and n_tup_del columns.
>>
>> If autovacuum_vacuum_threshold + (autovacuum_vacuum_scale_factor *
>> rows in the table) > n_dead_tup in pg_stat_user_tables, then the table
>> should be autovacuum'd.  If it hasn't yet reached this number, it
>> won't yet be a candidate.
>
> thanks for the explanation, now i understand. just to clarify: you
> probably meant
> the opposite, correct? when n_dead_tup is MORE than the threshold...

Erk, yes, switch the > to a <.

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Thom Brown
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