Re: Sudden drop in DBb performance

Hi,

On 03.09.2011 09:26, Gerhard Wohlgenannt wrote:
> Activating log_min_duration shows for instance this query --- there are
> now constantly queries which take absurdely long.

2 things you should check:

- if your /var/lib/postgresql is on an ext3 fs, I've seen such things
before due to the changes around Linux 2.6.2X that caused long stalls
during fsync() (see https://lwn.net/Articles/328363/ etc.). But if all
your queries take longer than they should and not only a few, that
probably isn't the reason.

- regarding your hardware RAID-5, I've seen some controllers switch the
write cache off quietly for various reasons (battery too old, issues
with disks). Check if it is still enabled, without write caching
enabled, most RAID-controllers will just suck.

Regards,
  Marinos