On 6/17/11 11:51 AM, Shianmiin wrote:
Tom Lane-2 wrote:
What's not apparent however is why the stats collector is writing disk
so much. 8.4 does have the logic change to not write stats out unless
something is asking to see them. So either it's really pre-8.4, or you
have a monitoring task that is constantly asking to see stats.
We have a PostgreSQL 9.0.4 on CentOs for performance testing and we are
seeing the similar issue.
we have a "crazy" setup it has 1 database with 1000 identical schemas. There
are occasional I/O write storm
of over 100 MB/sec without any disk reads, and it could last for a couple of
minutes when the schemas/data are aggressively populated by pg_restore. All
the io writes seem to be on pgstat.tmp.
The I/O write storm seemed to be trigger by Vacuum.
Based on the advice I got from my original question, I changed autovacuum_naptime to "5min", and the problem completely disappeared. (I know that's a long interval, but this particular server gets maybe 5-10 heavy updates per week and is idle the rest of the time.)
select count(1) from pg_database ;
count
-------
267
It seems like there's a problem somewhere. Autovacuum has improved enormously in the last couple of years, but some change to its algorithm causes a lot of I/O thrashing when there are more than a few hundred separate databases.
Craig
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