Re: Memory Limit Imposed on Oracle by Windows?

"BD" <robert.drea_at_gmail.com> wrote in message news:1176947912.694445.148860_at_y5g2000hsa.googlegroups.com...
> > could be 4GB or so. Is that true or is Oracle able to use as much of
the
> > available memory on the server as it is set up to use?
>
> The following applies to 32-bit Windows only.
>
> By default (without specific OS switches enabled), Windows is only
> able to directly 'see' (ie allow programs to access) 4GB. Anything
> above that is accessed via smoke and mirrors, similar to EMS/XMS in
> the DOS days. Virtual address spaces, yada yada yada.
>
> In fact, it is less - because the OS kernel must exist in the same
> 'base' region of memory. By default, Windows only allows programs
> direct access to *2* GB of RAM.
>
> This means that *all* Oracle instances must share that 2GB.
>
> There are two ways to address this - both involve OS switches, and one
> involves specific Oracle config changes.
>
> 1) The '/3GB' switch. Adding this switch to your boot.ini will cause
> the OS kernel to live in less memory (1GB), and allow programs direct
> access to 3GB of memory. This can obviously help, but may impose
> limitations on the OS side.
>
> 2) The '/PAE' switch. Adding this switch to your boot.ini will steal a
> small amount of base memory, which will then be converted into a
> 'mapping area' to the vast regions of memory above 4GB. It basically
> creates an extended address space (the acronym stands for Physical
> Address Extensions), and it lets Oracle use memory above the 4GB cap.
>
> ***however - you are limited to what can go into this upper region of
> memory - buffer cache only. The PGA, Shared Pool, all other memory
> areas must still exist in the base region of memory (be it 2 or 3GB).
>
> As well, you need to enable a parameter in Oracle:
> 'Use_indirect_data_buffers=TRUE'. This will allow the Oracle process
> to put the buffer cache up in higher memory. You must also assign a
> size for the 'mapping area' This parameter is 'AWE_WINDOW_SIZE', I
> believe.
>
> You must also change the terminology used in your pfile for the buffer
> cache size. Not the value, just the name. I forget the specific one
> there. But it's in the docs.
>
> One more thing: if you use *both* /3GB and /PAE on the same Windows
> box, you will *not* be able to see more than 16GB. Ever.
>
> Many hoops to jump through. I gather that these constraints are not
> present when using 64-bit Windows, but I don't know for sure.
>
> I also hear talk of performance issues when using /PAE in some cases.
> You must also be very aware that when using /3GB, you're forcing the
> OS kernel into a smaller region of memory.
>
> BD.
>

I'm probably restating the obvious but I just want to confirm what you're saying: if our system is 64-bit then we shouldn't have the limitations you mentioned above? Received on Wed Apr 18 2007 - 21:13:30 CDT