swapmem_on and nbuf kernel parameters.

[Gordon Brown_5]

I am running HP-UX 10.20 on a D390/2 with > 1Gb RAM. The swapmem_on parameter is set to 1 and the system has allocated 830Mb as memory swap of which it is actively using about 300Mb.

Would it be beneficial to turn swapmem off and set nbuf to a fixed size in order to return the large chunk of main memory for use by applications - specifically Oracle where I have a large SGA ( 220Mb).

In the past I have managed to squeeze just a bit more out of HP-UX by fixing nbuf but I have no experience of changing swapmem_on except on machines with > 3Gb RAM.

Any views welcome.

G

[James R. Ferguson]

Hi Gorden:

I would leave 'swapmem_on=1' to allow for processes adequate swapspace. I prefer to set 'bufpages' and 'nbuf' to zero (0) which enables dynamic buffer caching and set 'dbc_max_pct' to 5-10% with 'dbc_min_pct' to 2-5%.

...JRF...

[Rick Bowles]

Hi Gorden:

If you want a static buffer cache try nbuf=(0) and bufpages = (256 bufpages per 1mb of buffer cache). Try not to exceed 240mb of buffer cache.

You can monitor using sar -b 5 5 or Glance by selecting disk report (d) and forward to second page (f) and make sure you stay above 70 -75 % of read and write cache hits. Increase your buffer cache if need be. I like to average 90 - 99% cache hits.

[Naseemuddin Mohammed]

Hi
Gorden,

I think for Oracle you don't need to have large amount of swapmem, keep swapmem=1 but reduce dbc_max_pct to 10-15%.

[Ulf Lipski]

Hi all,

you must differ between swapping and file buffer memory usage. To have swapping in memory you set swapmem_on = 1, to get file buffer you must decide between static (nbuf)or dynamic (db_pct...). And if you need more memory for your database then reduce the parameters for the kernel above. In which order should I give as much memory as needed?
1. the database
2. the application
3. for file buffering
4. for swapping on memory

Hope this hint is usefull

[Shahul]

Hi

See this HTML which will talk more about configurable parameters.

Shahul