RE: linux kernel parameters

From: <dimensional.dba_at_comcast.net>
Date: Sat, 13 Feb 2021 10:20:48 -0800
Message-ID: <2b6401d70234$f4593180$dd0b9480$_at_comcast.net>



You have the relationship inverted in your statement.

"The problem is that SEMMNS has to be larger or equal than SEMMSL*SEMMNI"  

From Redhat

THE SEMMNS PARAMETER This parameter defines the total number of semaphores (not semaphore sets) for the entire Linux system. A semaphore set can have more than one semaphore, and as the semget(2) man page explains, values greater than SEMMSL * SEMMNI makes it irrelevant. The maximum number of semaphores that can be allocated on a Linux system will be the lesser of: SEMMNS or (SEMMSL * SEMMNI).   Again without the trace file we do not know what Oracle support was looking to change with those settings. If it is a semaphore problem and not a semaphore set or semaphore operation problem, then I would say that SEMMNS would also need to be increased to go along with the SEMMSL and SEMMNI increased settings. However, if the problem they are trying to fix is a semaphore set or semaphore operation problem then changing SEMMNS too, may not be necessary. Only the trace file or gdb of the core file will tell.      

From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> On Behalf Of Mladen Gogala
Sent: Saturday, February 13, 2021 9:57 AM To: dimensional.dba_at_comcast.net; oracle-l_at_freelists.org Subject: Re: linux kernel parameters  

The problem is that SEMMNS has to be larger or equal than SEMMSL*SEMMNI. Ideally, SEMMNS=SEMMSL*SEMMNI and SEMMSL=SEMOPM.

Semaphores are a subsystem governed by a device driver and have certain syntax. No recommendation which doesn't follow that syntax can be valid.

Regards

On 2/13/21 1:22 AM, dimensional.dba_at_comcast.net <mailto:dimensional.dba_at_comcast.net> wrote:

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.

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


--
http://www.freelists.org/webpage/oracle-l
Received on Sat Feb 13 2021 - 19:20:48 CET

Original text of this message