Help With Semaphores Increase

[Steven Chen_1]

Hi,

I experience problem on creating the 3rd Oracle instances and the errors indicate that my box of 2G memory needs to be adjusting on semaphores.

The followings are my info on the box, from which the 2 existing Oracle databases are working fine (just fails me to create another):

kmtune |grep -i sem
sema 1 - 1
semaem 16384 - 16384
semmap 1366 - (SEMMNI+2)
semmni 1364 - 1364
semmns 2048 - 2048
semmnu 683 - 683
semmsl 2048 Y 2048
semume 292 - 292
semvmx 32767 - 32767

Together the existing 2 database SGA use 650M/ea, and the buffer cache is 160M.

What value is safe to change on semmni, semmns...??

Very appreciated for quick help!

Steven

[Fred Ruffet · Accepted solution]

For each instance starting, Oracle verifies that it can create at least as many semaphores as the max number of processes it can open.

It mean that you must have semmns greater than the sum of the processes initialization parameter of all oracle instances

Regards,

[Rita C Workman]

One way is to check each instances init.ora for the amount of processes the file is requesting. Then add up for ALL the databases and put your semaphore values accordingly.

In your statement you say your trying to start a third instance and you already have 2 using 650 processes each..that's 1300 and based your parms, the third instance is probably tring to start when there are no resources left.
For myself...I add up all the semaphores and then just a 'little extra', for those peak times.

Rgrds,
Rita

[harry d brown jr]

You probably need to add more memory.

semaem Maximum: SEMVMX or 32767, whichever is smaller
semmap Maximum: Memory limited
semmni Maximum: Memory limited
semmns Maximum: Memory limited
semmnu Maximum: nproc-4
semmsl is the maximum number of semaphores per process
semume Maximum: SemMNS
semvmx Maximum: 65535

what are your dbc_max_pct & dbc_min_pct set to? Is bufpages and nbuf set to 0 (they should be)?

live free or die
harry

[Steven Chen_1]

Thanks for all help!

my bufpages and nbuf are set to 0, dbc_max_pct=8%, min=3%. The existing 2 db use 650M of memory each. They use 2000 processes in total.

If I need 400M of memory and 800 processes for the 3rd instance to be created successfully, what semaphores (in each) should I adjust, based on what I have?

Your further comment will be very appreciated.

[Fred Ruffet]

regarding IO cache settings, I would suggest you to mount the file systems for oracle with this options :
largefiles,convosync=direct,mincache=direct,nodatainlog
It will make oracle bypass the cache (it has its own) and will improve performances.

Regards,

Fred

[Fred Ruffet]

You will need to increase semmni to more than 2000+800 (3000 to be sure ?)

About memory, what physical memory have your server ?

Regards,

Fred

[Steven Chen_1]

Fred,

2G physical memory.

[Fred Ruffet]

So you'll have 1G out of 2 for Oracle SGA. Even if semxxx parameters are memory limited, you could increase semmns according to your needs (I have here a server with 2G, running with semmni=4096).

Regards,

Fred