[Hrgeeks] kernel.shmmax

[Erik Beebe]

Remember that shmmax is just setting the maximum possible shared memory 
segment - not how much memory you're actually reserving.  You'll do that 
when you configure the SGA in Oracle.  How large of an SGA you want may be 
left up to trial and error, but remember that the shadow processes (ie. 
the ones spawned per connection) use memory outside of the shared memory 
segment that you've reserved, so plan for that when deciding how much to 
leave remaining.

Also, Google for 'oracle rhel hugepages' or something similar, and 
consider using them, as they'll provide 2MB pages (vs. 4k), which makes 
for a much smaller page table with large memory allocations.

PS. The Linux virtual memory manager isn't that smart - consider setting 
vm.swappiness to 0 for a dedicated database server.

-Erik

On Fri, 9 Apr 2010, Matt Glaves wrote:

> As long as it's a dedicated DB box I think RAM-2GB left over for the base OS
> is what I'd start with.
>
> matt
>
>
> On Fri, Apr 9, 2010 at 12:29 PM, Erin <ewinningham at gmail.com> wrote:
>
>> Ok. I claim defeat. Will someone please explain kernel.shmmax and
>> kernel.shmall to me?  Specifically in relation to running Oracle on
>> RHEL5 64bit. It seems the OS sets it to 64GB even though the server
>> has 32GB of RAM. Tuned to RAM + reommended swap perhaps?  From what I
>> can tell Oracle recommends RAM - 2GB on 64bit systems.
>>
>> Discuss.
>>
>> Erin
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>