RE: linux kernel parameters

I know you didn't start the email thread. I try to tag onto the end of the email thread so as not to fracture the email thread into many subtrees. (Good email etiquette)  

As I stated what would be interesting is to see the trace file or run gdb on the core to determine what Oracle support saw that would make them put forth this as a solution.  

The two values they increased were SEMMSL SEMOPM. In the past on performance tuning linux the values for these two parameters were actually recommended at 8000+ on RHEL2-5).

Deciding to up the parameters to 3000 is not unheard of.

Oracle's recommendation on settings is a minimum value not an exact value relative to semaphore settings.

From the grid installation manual (Table B-3 Minimum Operating System Resource Parameter Settings) that match your values.

There are varying Documents in Oracle Support of Oracle troubleshooting problems and some of the values in the notes actually state the value for those 2 parameters can be up to 32000 on RHEL6 (Doc ID 2467427.1).

On most of the Exadatas I manage with out of the box settings (UEL6/7) those values are set to 2048.  

This is not unheard of and as long as they don't recommending setting the value beyond their numeric limit this is fine. This could be a work around to a bug or it is the new path going forward as a minimum.      

From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> On Behalf Of Mladen Gogala
Sent: Friday, February 12, 2021 9:15 PM
To: dimensional.dba_at_comcast.net; oracle-l_at_freelists.org Subject: Re: linux kernel parameters  

I am not the one who has started this thread but the setting of kernel.sem to 3000 32000 3000 128 makes no sense whatsoever. Interestingly enough, that recommendation increases the size of a semaphore set and the number of semaphore sets but it doesn't increase the number of semaphores. If the number of semaphores needs to be increased, the recommendation mentioned by Jeffrey is not the way to do that.

On 2/12/21 11:53 PM, dimensional.dba_at_comcast.net <mailto:dimensional.dba_at_comcast.net> wrote:

What was in the core file or trace files you uploaded for the SR. They may tell you why oracle is recommending increasing the values.

This could be a bug with rman that requires more semaphores than normal and this is their work around until they create a patch.  

-- 
Mladen Gogala
Database Consultant
https://dbwhisperer.wordpress.com


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