shared_buffers and Shared Memory Segments

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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


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