kcusage reading on dbc_max_pct

[Maximilian_1]

Hi,
I have 3 HPUX 11.23 servers running SSO application. The dbc_max_pct is set to 50 and when I check the system usage (kcusage), it is hitting 50/50. Is it normal?

When i check a few of other HPUX 11.23 servers running weblogic application servers, the readins is below 10 / 50.

Our phyiscal RAM is 4GB RAM

Anyone pls help. Thks

[Sung Oh]

Hello,

You can try to reduce the default size. also make sure you have dbc_min_pct is lower then dbc_max_pct size. default size is min/max = 5/50

you can use "kctune" to modify turn your kernel.

Regards,
Sung

[Senthil Kumar .A_1]

Hi,

Refer the below link, especially view the comments by

Steven E. Protter and
Jean-Luc Oudart

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=467288

regards,
Senthil Kumar .A

[Steven E. Protter]

Shalom,

To summarize,

dbc_max_pct and dbc_min_pct control the buffer cache for database and other server processes.

It is very expensive in CPU terms to change the amount of cache, so its best to keep these two figures in a tight range that works for your system.

Your software most likely has its own cache, designed for it. Its better to configure and use that.

SEP

[RAC_1]

What does following say?
sar -b 1 5, do you see %read and %write that are reasonable. The %write should at leat be around 90% or so, to get optimum from your buffer cache setting. 50% is default value.

[Rita C Workman]

The thread you were pointed to will help. Generally I go by...10% of whatever your physical memory is, but that's not a hard fast rule either.
At 4Gb memory you should be able to safely set yours to 10/5 for max/min.

There are a couple other things you might want to look at. Example if you let the formalae set certain parms, there will be a couple set to high. After dbc max/min I always look at ninode.
Run sar -v 1 10....look at the output. The left side says what you ARE using the right side of the column shows what you have it set at. Odds are you can reduce your ninode to 2048 or 4096.
Those sar commands are great for tuning things down...Remember a larger setting doesn't always mean you get more. Sometimes setting things 'down' is what gets better performance.

Kindest Regards,
Rita

[Maximilian_1]

hi All, Thks for the inputs.

However, when i look at the sar -b 1 5 output, i saw the pwrite is above 90%.
But my kcusage reading on dbc_max_pct always remains at 50(usage)/50(settings).
Does this means no need to tune?

I've recently upgraded my RAM on more than 10 hpux servers from 4 GB to 8GB, and some even higher to 16GBRAM.
Was pondering whether to set the dbc_max_pct to 10% of the Phyiscal RAM. If not, am afraid 50% of 16 GBRAM for buffer cache might affect the performance....But i set, worried performances drop cos these are production svrs and no load test is available...

Is it normal to tune down dbc_max_pct whenever we add more RAM?

[Steven E. Protter]

No Max.

I strongly urge you drop dbc_max_pct to 15 if you don't want to adjust dbc_min_pct

kctune can be used to do this on the fly in 11.23.

I just did this on an 11.23 system last week.

SEP

[Ninad_1]

Max,

I agree with Steven. For system with 8Gb or 16GB memory - setting dbc_max_pct to 50% is far too high and you should reduce it - in steps if possible to see the impact if any it has on your system functioning -

regards,
Ninad

[James George_1]

Hi

dbc_max_pct 50/50 is default. You should set to 10/5 which is normal. If you look at the top command, you will see a higher utilization of your CPUs , with this parameter set to 50/50. It basically reserves 50 % of your memory all the time. If you have multipe databse instances running, you would be in trouble with the CPUs hitting 100 %. So, change the settings , dbc_max_pct to 10 and dbc_min_pct to 5 or 2. This should release your memory for the processes.


rgds / james