Oracle IO Problems VA7400 or MOD12H

[Ray Brewer]

Sorry I forgot to mention about the timeslice parameter and to make sure it stays at 10. We have around 200 to 300 users at any given time on our databases. I feel you pain in not having time to recompile the kernel.

[Aziz Zouagui]

I will definitely change the timeslice parameter in the next Kernel rebuild.

Is there any other parameter in the list above, that need to be modified, Ray mentioned the DBC_MIN and DBC_MAX values.

Thank you very much everyone.

Aziz.

[harry d brown jr]

Aziz,

First, I'd set these so that the max of dbc_mac_pct would result in around 400M of you memory:

So if you have 4GB, set
dbc_max_pct 10
dbc_min_pct 2


Secondly, the va7400 is light years ahead of the 12H. I had one for 8 months as an evaluation and it rocked. Basically I set it up and walked away from it until I had to give it back to HP! Plus, you'll be switching from SCSI to fibre!


live free or die
harry

[Aziz Zouagui]

I have 8 Gig of RAM and 6CPU.

Do I double the values of dbc_min and max ?

[A. Clay Stephenson · Accepted solution]

If you have 8GB and you want to limit buffer cache to 400MB - a good value for 11.0 - then dbc_max_pct should be set to 5; 2 is okay for dbc_min_pct. In 10.20 and 11.0, you are actually going to see better performance in most cases by setting bufpages
to somewhere between 80000-100000 (320-400MB) and thus disabling dynamic buffer cache.

All of this pales, including faster disk arrays,
into insignificance compared to the effect of your current timeslice setting.

[Aziz Zouagui]

You all convinced me, I will change the following:

dbc_min_pct=2
dbc_max_pct=5
timeslice=10
bufpages=100000

Please let me know if there is anything else.

Thank you all.

aziz.

[A. Clay Stephenson]

There is no need to change the
dbc_xxx_pct values because when bufpages is set to a non-zero value, these parameters are ignored. I would also suggest that you consider installing PHKL_21678 (if applicable to your OS); the disk sort fairness algorithm could be one source of your problems. I wouldn't do the patch at this time because I think you are going to see a marked improvement from the timeslice setting. When that is done, you have a much better chance of correctly spotting other bottlenecks.

[Aziz Zouagui]

What about the nbuf parameter ?

I read somewhere that if you change the bufpages you also need to change the nbuf parameter.

[A. Clay Stephenson]

I had looked at your kernel parameters earlier. Your default setting of 0 for nbuf with a non-zero bufpages settings results in a a reasonable buffer header and pool allocation. It is rather rare that nbuf needs to be also adjusted.