On Fri, Sep 25, 2009 at 3:28 PM, Carlos Henrique Reimer
<carlos.reimer@opendb.com.br> wrote:
> Hi,
>
> We're facing performance problems in a Linux box running CentOS release 5
> (Final) and PostgreSQL 8.2.4. I've done some basic checks in the
> configuration but everything looks fine to me. One weird behaviour I've
> found is the cached size showed by the
> "top" and "free" Linux commands:
>
> top - 08:32:17 up 3 days, 19:04, 1 user, load average: 1.09, 1.07, 1.10
> Tasks: 173 total, 2 running, 170 sleeping, 0 stopped, 1 zombie
> Cpu(s): 9.5%us, 0.5%sy, 0.0%ni, 88.2%id, 1.7%wa, 0.0%hi, 0.0%si,
> 0.0%st
> Mem: 3631900k total, 3378056k used, 253844k free, 25488k buffers
> Swap: 4192956k total, 100k used, 4192856k free, 2356588k cached
>
> [postgres@server01 etc]$ free
> total used free shared buffers cached
> Mem: 3631900 3174804 457096 0 14280 2086184
> -/+ buffers/cache: 1074340 2557560
> Swap: 4192956 108 4192848
> [postgres@server01 etc]$
>
> Both commands show values ranging from 2GB to 2.3GB for the cached size and
> the server has 3.5GB RAM. I do usally see cached values with sizes bearing
> the size of the RAM in other servers. It seams that something is consuming
> the RAM and not letting it free to be used as cache for Linux files, right?
> The shared_buffers (256MB) is not high and I can not see a reason for this.
> Initially I've thought the problem was
> because the system was running with runlevel 5, but now, it's running with
> runlevel 3 and even so the values for
> cached size does not change.
>
> Any suggestions or directions I could follow to discover the reason?
If you run top, then hit M, and post the first 20 or so rows after
what you have here I can take a guess.