Thanks for your reply. I believe that the only possibility is autovacum activity I will check that. Anyway what puzzles me is that the throughput does not increase like i might expect if there where high VACUUM activity, only the WAIT TIME and thus the UTILIZATION. Is like if the disk/filesystem gets slower during one hour or so...
> Hi list, > > I am running Postgres 9.1 on Ubuntu 12.04. I have a dedicated disk for > pg_xlog, using ext4 filesystem with journaling in writeback mode > During high load times, the disk usage is arround 40%. The IO write time is > constant at about 3ms. On certain occasions roughly once in 15 days, the > IO write time goes up to about 10ms. This makes the disk usage go up to > almost 100%, probably saturation, and the INSERTS DELETES UPDATES run > considerable slower than normal.This lasts for about 2 hours and then the > latency goes back to 3ms and everything is normal again. > Has anyone seen this behavior? What could be causing the increase in > latency?
Can you correlate these episodes with autovacuum activity? Or perhaps backups are being taken (maybe a new base backup is taken every 15 days)? -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services