shared_buffers and Shared Memory Segments

Hello,

I am trying to understand the output of the 'ipcs' command during peak
activity and how I can use it to possibly tune the shared_buffers...

Here's what I see right now: (ipcs -m) - (Host is RHAS 3.0)

------ Shared Memory Segments --------

key shmid owner perms bytes nattch status

0x0052e2c1 1966080 postgres 600 92078080 322

What is nattch? Is this the num of segments attached? Is it saying that
about 92MB is used out of 512MB?

-Shared memory segment size is defined to be 512MB

-Currently, shared_buffers are at 80MB (10240)

Here's the 'top' output:

12:29:42 up 24 days, 15:04, 6 users, load average: 2.28, 1.07, 1.07

421 processes: 414 sleeping, 3 running, 4 zombie, 0 stopped

CPU states: cpu user nice system irq softirq iowait idle

total 83.6% 0.0% 40.8% 0.0% 7.6% 76.4% 190.0%

cpu00 20.9% 0.0% 9.0% 0.3% 0.1% 22.5% 46.8%

cpu01 19.2% 0.0% 10.6% 0.0% 7.3% 14.4% 48.3%

cpu02 15.0% 0.0% 7.3% 0.0% 0.0% 8.6% 68.9%

cpu03 28.6% 0.0% 14.0% 0.0% 0.1% 31.0% 26.0%

Mem: 7973712k av, 7675856k used, 297856k free, 0k shrd, 149220k
buff

3865444k actv, 2638404k in_d, 160092k in_c

Swap: 4096532k av, 28k used, 4096504k free 6387092k
cached

Can I conclude anything from these outputs and the buffer setting?

Appreciate any thoughts.

Thanks,
Anjan