Kernel parameter setting for rp5470

[Teresa Wong]

Hello,

I'm installing HP-UX 11i version 1 on a RP5470 server. An application client requested me to set the kernel parameter dnlc_hash_locks to "64", the default value for that is "512". When I try to lower it, system complained that the value 64 is less than the minimum value allow which is "128" and reject the request. Is there any way to force it down to 64. I'm not too sure what the impact will be to lower this value. Any help will be much appreciated. Thanks

Regards
Teresa

[Tom Smith_9]

Teresa,
I would leave dnlc_hash_locks at the default of 512. Generally an application will work properly if the parameter in question is larger than the specified value, especially if that value is a default.

Hope this helps.
-Tom

[Steven E. Protter]

You may be misinterpreting the instructions for the application.
In general with this parameter the instructions say the minimum value is 64. Any value above that is usaly acceptable to the application.

This parameter is formula based on my HP-9000 system in HP class. You can use sam to change the formula so that you get a value of 64. My system has dnlc_hash_locks set to 64. So it can be done

I woud suggest sam kernel configurable parameters.

Then you get an explanation that wil make the change more meaningful.

If you want to keep the formula, you may need to change the value of the two parameters used to calculate dnlc_hash_locks.

SEP

[Helen French]

Normally, it's NOT a good practice to forcefully lower a kernel parameter value than it's minimum value! I don't think you can even do that. If you think it's reasonable to reduce the value from it's default, fix it to minimum allowed.

This kernel parameter is the value of number of lock groups in a DNLC (Directory Name lookup cache in Kernel) chain. Lowering this value will free some memory (since the DNLC cache is residing on the memory), but may impact performance during large number of filename accesses.

You can read more about this parameter on www.docs.hp.com

[Pete Randall]

SEP must be on a 11.0 machine where the minimum value is 16. On 11i machines Teresa is absolutely right - the minimum is 128. I agree that it should be left alone. The application should be specifying a minimum and there is no way that I can see an excess of hash locks having an adverse effect.


Pete

[Teresa Wong]

Thanks for the suggestion, just out of curiosity, when I use SAM to try change the dnlc_hash_locks, it's not based on formula but just a value. Can you tell me which parameter does it depend on?? Thanks

Regards
Teresa

[Helen French]

For the last question: It depend on a parameter called 'ncsize'.

ncsize >= 8 x dnlc_hash_locks