Re: 32 bit and 64 bit memory

Windows is a mess. Everything (all foreground and background processes) has to cram inside 2Gb (default) or 3Gb (boot.ini option for certain Windows versions). Also, by default, each database session thread allocates 1Mb for stack space by default, and that takes away from the process's total of 2-3Gb memory. That default can be adjusted downward (no lower than 512Kb recommended) using an Oracle-supplied program called ORASTACK. Also, there is some capability to exceed the 2-3Gb limit for the Buffer Cache only (not the whole SGA, just the Buffer Cache) to extend into AWE (forget exactly what the acronym means - something like "advanced windows extensions") memory, but the extended AWE memory involves some indirection so it is "slower" to access or manipulate than "regular" memory. Just a kludge all round, because Windows can't/won't support shared memory or semaphore constructs...

...believe me all you Windows folks -- it is nothing personal. But Windows should be far better than this, with only one vendor calling the shots...

32-bit UNIXs can accomodate 2-4Gb per process. Each foreground and background Oracle server process gets its own allocation of 2-4Gb, so you can pretty much go nuts and chew up as much memory as you please. The sticking point behind the 2-4Gb limit is the shared-memory used for the SGA, which counts toward each processes' total. So, if you have a 1.6Gb SGA and the UNIX variant you are using is limited to 2Gb, then everything else (i.e. stack, PGA, UGA) has to fit into 0.4Gb. Luckily, that's usually not a problem. But sometimes a larger SGA is a legitimate need...

The 64-bit UNIXs can accomodate something like 64Pb of data. That's peta-bytes, a.k.a. 1,024 tera-bytes, a.k.a. 1,048,576 giga-bytes. I'm not aware of any server on the planet (or off the planet but nearby) with even 1Tb of physical RAM (though that doesn't mean there aren't), so 64-bit OSs should eliminate any restrictions on virtual memory, at least for the next couple years...

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Friday, February 28, 2003 10:34 AM

> Hello,
>
> 1) How big (max) can an Oracle SGA be in a 32bit platform (Windows and
> Linux on ia32)?
>
> 2) How big (max) can an Oracle SGA be on a 64bit platform (Sparc
> Solaris, AIX PowerPC)?
>
> Thanks.
>
> --
> Lyndon Tiu
>
>
>
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
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> Author: Lyndon Tiu
> INET: ltiu_at_alumni.sfu.ca
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