RE: Linux LowMem errors

I had a similar problem with OOM errors on a RH 3 box running an smp kernel, with 9i RAC DB's  

Every week I had DB's crashing with

ORA-27504: IPC error creating OSD context, and other OOM errors  

Setting the following kernel parameter helped for while, then every few weeks my load would shoot through the roof 150+, then die

vm.vm-defragment = 1000  

Using the hugemem kernel has fixed the problem here, for now at least.

I'm migrating to 64 now.  

and since your already on hugemem, any patches will only be bandaid solutions.

The only way you truly fix the problem though is to migrate to 64bit  

David Hill

Oracle DBA    

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Niall Litchfield Sent: Monday, February 11, 2008 5:20 AM
To: tim_at_evdbt.com
Cc: Oracle List
Subject: Re: Linux LowMem errors  

Not that MTU! There's an Oracle patch which has the following effect

        change skgxp MTU from 32k to 16k

What seems to be happening is that Oracle requests 32k chunks of memory from the OS for (I think) IPC packets. The bug description suggests that Linux is somewhat prone to low memory fragmentation and isn't able to allocate the memory.  

On Feb 10, 2008 3:59 PM, Tim Gorman <tim_at_evdbt.com> wrote:

        MTU of 32768 sounds interesting -- usually it is set to 1500, occasionally 9000. Not sure if this is significant, and I could be misinterpreting "requirement" for "setting" or some such, but I thought worth noting...                                    

        Niall Litchfield wrote:

        We've recently updated some of our RH database servers to kernel 2.4.21-53ELHugemem and have experienced problems with the databases and ASM instances crashing and huge numbers (like 80,000) yesterday on one box of core dumps. The crashes did not occur immediately after the kernel update, but that is AFAIK the only significant recent change. The head of the trace reads          

        SKGXPVFYMMTU: Could not create context which satisfies the minimum

        MTU requirement of 32768 bytes

        kgefec: fatal error 0

• 2008-02-09 07:29:39.767

        ksedmp: internal or fatal error

        ORA-00603: ORACLE server session terminated by fatal error

        ORA-27504: IPC error creating OSD context

        ORA-27300: OS system dependent operation:sendmsg failed with status: 12

        ORA-27301: OS failure message: Cannot allocate memory

        ORA-27302: failure occurred at: sskgxpsnd1         

        which looks significantly like the issue addressed in Note 419871.1. to me. Has anyone else come across these issues?

	-- 
	Niall Litchfield
	Oracle DBA
	http://www.orawin.info <http://www.orawin.info/>  

-- 
Niall Litchfield
Oracle DBA
http://www.orawin.info 


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