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    Memory Limitations on Windows x64

    754415
      I know that on x86 Windows there are rather constricting size limitations for various memory settings in the database (I'm primarily concerned with SGA and PGA) per this note. I would like to know if these same limitations pertain to Windows x64 OS as well?

      Sorry, but the note was last modified in October 2009 so it's misleading.

      Thanks,

      John

      Edited by: CJohnRun on Mar 1, 2010 10:20 AM
        • 1. Re: Memory Limitations on Windows x64
          Charles Hooper
          Assuming that you do not plan to use Oracle XE, Oracle Database will be limited by the amount of memory that the physical hardware can support (Ex: 16 memory slots, multilplied by whatever is the largest support amount of memory card per slot) and the release version of Windows. See the following document for the limitations of various versions of Windows:
          http://msdn.microsoft.com/en-us/library/aa366778(VS.85).aspx#physical_memory_limits_windows_server_2008_r2

          Charles Hooper
          Co-author of "Expert Oracle Practices: Oracle Database Administration from the Oak Table"
          http://hoopercharles.wordpress.com/
          IT Manager/Oracle DBA
          K&M Machine-Fabricating, Inc.
          • 2. Re: Memory Limitations on Windows x64
            754415
            I don't believe that's entirely true as x86 Windows 2003 Enterprise OS (which is the OS in question) can support up to 64GB of RAM with PAE enabled, but all of my attempts at increasing the SGA/PGA size over 4GB is in vain as stated in this note (46001.1). Will I run into these same issues with x64 Windows or not? I'm asking because I do not want to rebuild the OS as x64 just to run into the same issues.

            Thanks again,

            John
            • 3. Re: Memory Limitations on Windows x64
              Centinul
              CJohnRun wrote:
              I don't believe that's entirely true as x86 Windows 2003 Enterprise OS (which is the OS in question) can support up to 64GB of RAM with PAE enabled, but all of my attempts at increasing the SGA/PGA size over 4GB is in vain...
              Even though the OS can support up to 64GB of RAM the user process space is still under the 32-bit limit.
              PAE does not change the amount of virtual address space available to a process. Each process running in 32-bit Windows is still limited to a 4 GB virtual address space.
              Source: http://msdn.microsoft.com/en-us/library/aa366796%28VS.85%29.aspx
              • 4. Re: Memory Limitations on Windows x64
                754415
                Correct, I get that, but back to my question, does this also apply if the OS is 64 bit?
                • 5. Re: Memory Limitations on Windows x64
                  Centinul
                  CJohnRun wrote:
                  Correct, I get that, but back to my question, does this also apply if the OS is 64 bit?
                  No.
                  Virtual Address Space
                  By default, 64-bit Microsoft Windows-based applications have a user-mode address space of 8 terabytes>

                  Source: http://msdn.microsoft.com/en-us/library/aa384271%28VS.85%29.aspx
                  • 6. Re: Memory Limitations on Windows x64
                    754415
                    Do you know if there are any Oracle notes/documentation/etc. to that effect?
                    • 7. Re: Memory Limitations on Windows x64
                      Centinul
                      Not sure what you are after exactly, but for your Oracle version do the following:

                      1. Go to http://tahiti.oracle.com
                      2. Click on your version.
                      3. Click on "Books"
                      4. Find the one titled Reference
                      5. Find the chapter named "Database Limits"
                      6. Find the section called "Process and Runtime Limits"

                      It should say something like the following:
                      SGA size      Maximum value      Operating system-dependent; typically 2 to 4 GB for 32-bit operating systems, and > 4 GB for 64-bit operating systems
                      • 8. Re: Memory Limitations on Windows x64
                        754415
                        "Operating system-dependent" is the part I'm concerned about. Any other documentation with specific reference about Windows x64 OS's? If not, I guess this will have to suffice with moving the rebuild along.
                        • 9. Re: Memory Limitations on Windows x64
                          Centinul
                          I'm sorry, but I'm not sure where the concern is.

                          I've pointed you to MS documentation that says the user address space for x64 systems is 8 terabytes. Oracle says that on x64 systems the SGA can be > 4 GB.

                          You should be all set :)
                          • 10. Re: Memory Limitations on Windows x64
                            754415
                            My concern stems from the fact that note 46001.1 doesn't specifically mention x86 or x64 Winows. It reads as a general overview of Windows NT Memory Architecture, and the one sentence where x64 is mentioned:
                            Although the ultimate solution will come when Windows supports a 64-Bit virtual address model.
                            is even more misleading as Windows has had x64 Operating Systems out for the better part of a decade.

                            So, hence my concerns. Rebuilding a few OS's won't kill us on time, but if I run into the same 4GB memory limitation it'll be a complete waste of my time.

                            Thanks for the help,

                            John
                            • 11. Re: Memory Limitations on Windows x64
                              Charles Hooper
                              CJohnRun wrote:
                              I don't believe that's entirely true as x86 Windows 2003 Enterprise OS (which is the OS in question) can support up to 64GB of RAM with PAE enabled, but all of my attempts at increasing the SGA/PGA size over 4GB is in vain as stated in this note (46001.1). Will I run into these same issues with x64 Windows or not? I'm asking because I do not want to rebuild the OS as x64 just to run into the same issues.

                              Thanks again,

                              John
                              Please see the document that I linked to in my original reply. The Standard Edition of 64 bit Windows 2003/2008 Server is artifically limited to 32GB in a flat memory model. The Enterprise Edition of 64 bit Windows 2003/2008 Server supports more memory than you can physically connect to the server's motherboard. 64 bit Oracle Database Standard Edition One and greater is able to take advantage all of the memory in the server that is provided within the flat memory model without any special configuration - other than enabling large page support to decrease the overhead of managing a lot of memory.

                              The problem that you are encountering with 32 bit Windows is a limitation of 32 bit software - it can only address 2^32 GB of memory - that is 4GB. To access more than 4GB, a memory region is set aside to act as a translation window to peek into the upper memory region which can contain only the Oracle buffer cache. Articles on Metalink describe how this works. The 64 bit flat memory model does not have this limitation. With 64GB in the server, you could specify a 32GB SGA_TARGET and 20GB PGA_AGGREGATE_TARGET, if you so desire.

                              Charles Hooper
                              Co-author of "Expert Oracle Practices: Oracle Database Administration from the Oak Table"
                              http://hoopercharles.wordpress.com/
                              IT Manager/Oracle DBA
                              K&M Machine-Fabricating, Inc.
                              • 12. Re: Memory Limitations on Windows x64
                                754415
                                Charles,

                                I appreciate the expanded explanation, but the reason why I kept probing for more answers is that you provided me with a MS link. It looks like the best thing that I'm finding from Oracle is the Certifications tab in Metalink.

                                Thanks,

                                John
                                • 13. Re: Memory Limitations on Windows x64
                                  754415
                                  Metalink -> Certifications Tab -> Fill in appropriate info and look for Certified platforms.
                                  • 14. Re: Memory Limitations on Windows x64
                                    Hans Forbrich
                                    CJohnRun wrote:
                                    Charles,

                                    I appreciate the expanded explanation, but the reason why I kept probing for more answers is that you provided me with a MS link. It looks like the best thing that I'm finding from Oracle is the Certifications tab in Metalink.
                                    You might also get related information in the doc set (ref tahiti.oracle.com above). The more useful doc is the 'Platform Guide for Windows' which discusses the various limits that the Reference manual says are platform specific.

                                    Unfortunately the Platform Guide (and the *nix counterpart - Administrator's Reference) tend to be hidden - look for them in the Master book list.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
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