Re: Postgres Performance Tuning

On Mon, Apr 4, 2011 at 5:34 AM, Adarsh Sharma <adarsh(dot)sharma(at)orkash(dot)com> wrote:
> Mem:  16299476k total, 16198784k used,   100692k free,    73776k buffers
> Swap: 16787884k total,   148176k used, 16639708k free, 15585396k cached
>
>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+
> COMMAND
>  3401 postgres  20   0 4288m 3.3g 3.3g S    0 21.1   0:24.73
> postgres
>  3397 postgres  20   0 4286m 119m 119m S    0  0.8   0:00.36
> postgres
> PLease help me to understand how much memory does 1 Connection Uses and how
> to use Server parameters accordingly.

OK, first, see the 15585396k cached? That's how much memory your OS
is using to cache file systems etc. Basically that's memory not being
used by anything else right now, so the OS borrows it and uses it for
caching.

Next, VIRT is how much memory your process would need to load every
lib it might need but may not be using now, plus all the shared memory
it might need, plus it's own space etc. It's not memory in use, it's
memory that might under the worst circumstances, be used by that one
process. RES is the amount of memory the process IS actually
touching, including shared memory that other processes may be sharing.
Finally, SHR is the amount of shared memory the process is touching.
so, taking your biggest process, it is linked to enough libraries and
shared memory and it's own private memory to add up to 4288Meg. It is
currently actually touching 3.3G. Of that 3.3G it is touching 3.3G is
shared with other processes. So, the difference between RES and SHR
is 0, so the delta, or extra memory it's using besides shared memory
is ZERO (or very close to it, probably dozens or fewer of megabytes).

So, you're NOT running out of memory. Remember when I mentioned
iostat, vmstat, etc up above? Have you run any of those?