Effect Of Multiple SHMMAX Settings

Last week I saw a warning message at database startup time saying:

WARNING: EINVAL creating segment of size 0x000000000f0020xx
fix shm parameters in /etc/system or equivalent 

It is an Oracle 10204 database running on Solaris.

Searching MOS for exact meaning for this warning, it states that a new shared memory segment is getting created to accommodate SGA.

As the message indicated, I opened /etc/system file to verify the settings of SHMMAX parameter and found the SHMMAX value to be 4GB. I stopped at this point and closed the /etc/system file. Then the next thing to check is the number of oracle instances running on the server and the size of largest SGA.

There were two instances running on the server and the largest SGA was set to 1.8G and the other SGA size was 700M.

This setting shows that there is no need to create additional shared memory segment. Then I checked the /etc/system file again, but this time I used the following command :

<span style="font-size: small;"><span style="font-family: arial,helvetica,sans-serif;">$ cat /etc/system | grep shmmax</span></span>
<span style="font-size: small;"><span style="font-family: arial,helvetica,sans-serif;">set shmsys:shminfo_shmmax=4000000000  ==&gt;4GB</span></span>
<span style="font-size: small;"><span style="font-family: arial,helvetica,sans-serif;">set shmsys:shminfo_shmmax=500000000  ==&gt;500M</span></span><span style="font-size: small;"><span style="font-family: arial,helvetica,sans-serif;">

There were two different values set for SHMMAX parameter.

The cause of the above warning message came out to be:
As the files are read from bottom-to-top, server was taking SHMMAX value as 500M and ignoring the 4GB value.

After commenting SHMMAX value of 500M, the warning message disappeared.

Tags: 10gdatabaseUnix