topic Re: Problems with SWAP in Operating System - HP-UX

Problems with SWAP

Fernando Jose P de Souz — Thu, 21 Jul 2005 04:33:43 GMT

Hi,

I have a doubt about my server HP-UX 11.23, Oracle database 9.2.0.1.0.

The server isn't using the swap area, when the physical memory is 100%,
the server don't allocate any processes.

i create 2 secondary swap to performe the swap and the system.

Where could i set to the system use the swap area in HP-UX????
or could i set the swap area to use in the oracle?

# swapinfo -tam

Mb Mb Mb PCT START/%
TYPE AVAIL USED FREE USED%
dev 4096 142 3954 3%
dev 1000 141 859 14%
dev 1000 141 859 14%
reserve - 5611 -5611 %
memory 4085 3321 764 81%
total 10181 9356 825 92%

Fernando.

Re: Problems with SWAP

Pete Randall — Thu, 21 Jul 2005 04:44:36 GMT

Things actually may be running just the way they are supposed to. Try running "vmstat 1 5" and observe the "po" column. If there is little or no page outs going on, then you are in good shape - your memory utilization is high, but you're not swapping and that's what you want.

Pete

Re: Problems with SWAP

Thayanidhi — Thu, 21 Jul 2005 05:12:00 GMT

Hi,
You should be happy if there is no swap activity. 100% could be normal becuase dbc_max_pct value in kernel. Means what ever free memory you have is set as cache depends on this parameter. As long as there is no page out (po in vmstat output) you are fine.

Regds
TT

Re: Problems with SWAP

Marek Smejkal — Thu, 21 Jul 2005 05:13:28 GMT

Fernando,

If your memory usage is this high, you should get more memory, if you start swapping the performance will go down.
Marek

Re: Problems with SWAP

Cem Tugrul — Thu, 21 Jul 2005 05:24:39 GMT

Fernando,

Best systems do not use swap area even swap area defined.On the other hand,there are
2 important kernel parameters when you have
Oracle,

dbc_max_pct
dbc_min_pct

dbc_max_pct Max dynamic Buffer Cache size in percent
of system memory, when bufpages and
nbuf are both set to 0.
Do not set this value to high, it will use this percentage of the memory to file system cache and give it not to Oracle or any other application!!!!
default=50.
recommended: between 3 and 10 % of the memory
It's more efficient to use system memory
for Oracle SGA instead of file system
buffer cache

dbc_min_pct Min dynamic Buffer Cache size in percent
of system memory (see dbc_max_pct),
default=5.
recommended: between 2 and 5

Good Luck,

Re: Problems with SWAP

Cem Tugrul — Thu, 21 Jul 2005 05:38:09 GMT

Let's say you have 16Gb physical ram so
when you set;

dbc_max_pct 4
dbc_min_pct 2

it means your system is going to use maximum
%4 of physical ram (640MB) for buffer cache
so also use minumum %2 physical ram (320Mb)

That's the trick when you have more than
12Gb physical ram.

When you are in this situation i also advise
you to increase shmax parameter so this also
effect your SGA and then go to increase your
Oracle SGA.

Good Luck,