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Postgres 9.1.4 - high stats collector IO usage

From: David Barton <dave(at)oneit(dot)com(dot)au>
To: pgsql-performance(at)postgresql(dot)org
Subject: Postgres 9.1.4 - high stats collector IO usage
Date: 2012-07-28 04:33:17
Message-ID: 50136B8D.7070502@oneit.com.au (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,

I am running postgres 9.1.4 on Ubuntu 12.04 and the stats collector is 
generating very high IO usage even when nothing appears to be happening 
on the system.

I have roughly 150 different databases, each of which is running in 1 of 
roughly 30 tablespaces.  The databases are small (the dump of most is 
are under 100M, and all but 3 are under 1G, nothing larger than 2G).

Previously iotop reported the disk write speed, at ~6MB / second.  I 
went and reset the stats for every database and that shrunk the stats 
file and brought the IO it down to 1MB / second.  I still think this is 
too high for an idle database.  I've now noticed it is growing.

ls -l /var/lib/postgresql/9.1/main/pg_stat_tmp/pgstat.stat
-rw------- 1 postgres postgres 3515080 Jul 28 11:58 
/var/lib/postgresql/9.1/main/pg_stat_tmp/pgstat.stat

*<reset of stats> *

ls -l /var/lib/postgresql/9.1/main/pg_stat_tmp/pgstat.stat
-rw------- 1 postgres postgres 514761 Jul 28 12:11 
/var/lib/postgresql/9.1/main/pg_stat_tmp/pgstat.stat

*<watch the file grow>*

ls -l /var/lib/postgresql/9.1/main/pg_stat_tmp/pgstat.stat
-rw------- 1 postgres postgres 776711 Jul 28 12:25 
/var/lib/postgresql/9.1/main/pg_stat_tmp/pgstat.stat

In the 15 minutes since the reset, IO has nearly doubled to 1.6+ MB / 
second.

FWIW, I just migrated all these databases over to this new server by 
restoring from pg_dump  I was previously experiencing this on 8.3, which 
was why I upgraded to 9.1 and I also have another server with similar 
problems on 9.1.

Any help would be sincerely appreciated.


David Barton dave(at)oneit(dot)com(dot)au

Responses

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Next:From: Pavel StehuleDate: 2012-07-28 07:07:48
Subject: Re: Postgres 9.1.4 - high stats collector IO usage
Previous:From: Anibal David AcostaDate: 2012-07-27 22:31:21
Subject: Re: pgstat wait timeout

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