Re: Memory reporting on CentOS Linux - Mailing list pgsql-performance

On Fri, 2009-08-14 at 14:00 -0400, Jeremy Carroll wrote:
> I am confused about what the OS is reporting for memory usage on
> CentOS 5.3 Linux. Looking at the resident memory size of the
> processes. Looking at the resident size of all postgres processes, the
> system should be using around 30Gb of physical ram. I know that it
> states that it is using a lot of shared memory. My question is how to
> I determine how much physical RAM postgres is using at any point in
> time?
>
> This server has 24Gb of ram, and is reporting that 23GB is free for
> use. See calculation below
>
> (Memory Total –  Used) + (Buffers + Cached) = Free Memory
> (24675740 – 24105052) +  (140312 + 22825616) = 23,536,616 or ~23
> Gigabytes
>
you're using cached swap in your calculation ( 22825616 )  swap is not
RAM -- it's disk


>
> So if my server has 23Gb of ram that is free for use, why is postgres
> reporting resident sizes of 30GB? Shared memory is reporting the same
> values, so how is the OS reporting that only 1Gb of RAM is being used?

you have 570688k free RAM + 140312k buffers RAM
This looks to me like the OS is saying that you are using 24105052k used
>
> Help?
>
> top - 12:43:41 up 2 days, 19:04,  2 users,  load average: 4.99, 4.81,
> 4.33
> Tasks: 245 total,   4 running, 241 sleeping,   0 stopped,   0 zombie
> Cpu(s): 26.0%us,  0.0%sy,  0.0%ni, 73.9%id,  0.1%wa,  0.0%hi,  0.0%
> si,  0.0%st
> Mem:  24675740k total, 24105052k used,   570688k free,   140312k
> buffers
> Swap:  2097144k total,      272k used,  2096872k free, 22825616k
> cached
> ---------------------
> PID     USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+
>  COMMAND
> 19469 postgres  15   0 8324m 7.9g 7.9g S  0.0 33.7   0:54.30 postgres:
> writer process
>
> 29763 postgres  25   0 8329m 4.5g 4.5g R 99.8 19.0  24:53.02 postgres:
> niadmin database x.x.x.49(51136) UPDATE
> 29765 postgres  25   0 8329m 4.4g 4.4g R 99.8 18.8  24:42.77 postgres:
> niadmin database x.x.x.49(51138) UPDATE
> 31778 postgres  25   0 8329m 4.2g 4.2g R 99.5 17.8  17:56.95 postgres:
> niadmin database x.x.x.49(51288) UPDATE
> 31779 postgres  25   0 8329m 4.2g 4.2g R 99.1 17.8  17:59.62 postgres:
> niadmin database x.x.x.49(51289) UPDATE
> 31780 postgres  23   0 8329m 4.1g 4.1g R 100.1 17.5  17:52.53
> postgres: niadmin database x.x.x.49(51290) UPDATE
> 19467 postgres  15   0 8320m 160m 160m S  0.0  0.7
>   0:00.24 /opt/PostgreSQL/8.3/bin/postgres
> -D /opt/PostgreSQL/8.3/data
> 19470 postgres  15   0 8324m 2392 1880 S  0.0  0.0   0:01.72 postgres:
> wal writer process