Re: Maximum number of Oracle instances on Windows

  • From: De DBA <dedba@xxxxxxxxxx>
  • To: peter.schauss@xxxxxxx
  • Date: Mon, 22 Sep 2014 10:24:17 +1000

Hi Peter,

I usually find memory constraints the most challenging when configuring databases on 
Windows. Per-process memory should not be a problem unless the /LARGEADDRESSAWARE 
<http://go.microsoft.com/FWLink/p/?LinkID=132948> option is cleared, in which 
case an instance cannot use more than 2GB. This is an issue as on Windows, unlike 
Unix, all Oracle processes run as threads in the same memory space (including client 
server processes).

If you want to load all SGAs into memory at the same time, you should also pay 
attention to the different Windows versions, as the supported amount of 
physical memory is limited on various editions, e.g. 32GB for the 2008R2 
standard edition.

You can find the per-process memory and physical memory limits at: 
http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx#memory_limits
 and 
http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx#physical_memory_limits_windows_server_2008_r2

Cheers,
Tony

On 20/09/14 05:38, Schauss, Peter (ESS) wrote:
One of the sites that I support has asked me to spec out new production and 
dev/qa database servers.  They are currently running Windows.  On the 
production server they expect to have 15 or 16 small Oracle instances with a 
total SGA+PGA  of 35 gb.  About half of their instances are at 11.1 but they 
well be eventually upgrading all of them to 11.2.  If we go with Windows for 
the new servers we will be running Windows Server 2008r2 64 bit.

I would, obviously like to move them to Linux, but I expect that they will 
resist the idea.  Are we going to run into any absolute or practical limits 
running 15 or 16 Oracle instances with 35 gb of memory on a Windows server?

Thanks,
Peter Schauss
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