Обсуждение: Autovacuum Issue

Hi,

My application is performing 1600 inserts per second and 7 updates per second. The updates occurred only in a small table which has only 6 integer columns. The inserts occurred in all other daily tables. My application creates around 75 tables per day. No updates/deletes occurred in those 75 daily tables (only inserts and drop tables if older than 40 days). Since only inserts in the daily tables, I disabled autovacuum in the conf file and I can see it is off stat using show command.

sasdb=# show "autovacuum";
 autovacuum
------------
 off
(1 row)

But the autovacuum is running frequently and it impact the performance of my system(high CPU). You can see the autovacuum in the pg_stat_activity.

sasdb=# select current_query from pg_stat_activity where current_query like 'autovacuum%';
                                     current_query                                    
---------------------------------------------------------------------------------------
 autovacuum: VACUUM public.xxxxx_17_Oct_11 (to prevent wraparound)
 autovacuum: VACUUM public.xxxxx_17_Oct_11 (to prevent wraparound)
 autovacuum: VACUUM public.xxxxx_17_Oct_11 (to prevent wraparound)
(3 rows)


Why the autovacuum is running even though, I disabled ? Am I miss anything ?

And also please share your views on my decision about disable autovacuum for my application. I am planning to run vacuum command daily on that small table which has frequent updates.

Thanks,
Ramesh

On Wed, Nov 23, 2011 at 12:55 AM, J Ramesh Kumar <rameshj1977@gmail.com> wrote:
> Why the autovacuum is running even though, I disabled ? Am I miss anything ?

As Raghavendra says, anti-wraparound vacuum will always kick in to
prevent a database shutdown.

> And also please share your views on my decision about disable autovacuum for
> my application. I am planning to run vacuum command daily on that small
> table which has frequent updates.

Sounds like a bad plan.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

On 02/12/11 07:18, Robert Haas wrote:
>
> And also please share your views on my decision about disable autovacuum for
> my application. I am planning to run vacuum command daily on that small
> table which has frequent updates.
> Sounds like a bad plan.
>

If the table has frequent updates vacuuming once a day will not control
space bloat from dead rows... so your small table's storage will become
a very large (even though there are only a few undeleted rows), and
performance will become terrible.

I would suggest tuning autovacuum to wakeup more frequently (c.f
autovacuum_naptime parameter), so your small table stays small.

Also you didn't mention what version of Postgres you are running. In 8.4
and later vacuum (hence autovacuum) is much smarter about finding dead
rows to clean up, and should have less impact. You can also control the
load autovacuum puts on your system (c.f autovacuum_vacuum_cost_delay
parameter).

regards

Mark

On Tue, Nov 22, 2011 at 10:55 PM, J Ramesh Kumar <rameshj1977@gmail.com> wrote:
> But the autovacuum is running frequently and it impact the performance of my
> system(high CPU). You can see the autovacuum in the pg_stat_activity.

Could you show us the system metrics that led you to believe it was
high CPU usage?  Sometimes people misinterpret the numbers from
utilities like top, iostat, or vmstat, so I'd rather see them myself
if you got them.