6 Replies Latest reply: Oct 18, 2012 4:33 PM by Catch-22 RSS

    11.2.0.3 on OEL Linux - are huge pages finally compatible with AMM?

    user5749629
      In light of article "USE_LARGE_PAGES To Enable HugePages In 11.2 [ID 1392497.1]" which explains that 11.2.0.3 can use both huge and kernel pages simultaneously - is AMM now compatible with huge pages? In other words - can you create a certain amount of huge pages, bring up Oracle with USER_LARGE_PAGES=AUTO, and have Oracle use large pages to the extent that they are available and spill to kernel pages when they are exhausted and/or for everything else?

      A way to keep AMM's valuable memory management while enjoying the efficiency of huge pages?
        • 1. Re: 11.2.0.3 on OEL Linux - are huge pages finally compatible with AMM?
          sb92075
          Handle:     user5749629
          Status Level:     Newbie
          Registered:     Apr 14, 2010
          Total Posts:     17
          Total Questions:     5 (5 unresolved)

          why do you waste time here when you never get answers to any of your questions?
          • 2. Re: 11.2.0.3 on OEL Linux - are huge pages finally compatible with AMM?
            rp0428
            >
            is AMM now compatible with huge pages?
            >
            No - but Automatic Shared Memory Management and Automatic PGA Management are.

            See the Database Administrator's Reference
            11g Release 2 (11.2) for Linux and UNIX-Based Operating Systems

            http://docs.oracle.com/cd/E11882_01/server.112/e10839/appi_vlm.htm#CACDCGAH
            >
            G.2.3 Restrictions for HugePages Configurations
            Following are the limitations of using HugePages:

            •The Automatic Memory Management (AMM) and HugePages are not compatible. With AMM the entire SGA memory is allocated by creating files under /dev/shm. When Oracle Database allocates SGA that way HugePages are not reserved. You must disable AMM on Oracle Database to use HugePages.

            •If you are using VLM in a 32-bit environment, then you cannot use HugePages for the Database Buffer cache. HugePages can be used for other parts of SGA like shared_pool, large_pool, and so on. Memory allocation for VLM (buffer cache) is done using shared memory file systems (ramfs/tmpfs/shmfs). HugePages does not get reserved or used by the memory file systems.

            •HugePages are not subject to allocation or release after system startup, unless a system administrator changes the HugePages configuration by modifying the number of pages available, or the pool size. If the space required is not reserved in memory during system startup, then HugePages allocation fails.
            • 3. Re: 11.2.0.3 on OEL Linux - are huge pages finally compatible with AMM?
              Billy~Verreynne
              sb92075 wrote:
              Handle:     user5749629
              Status Level:     Newbie
              Registered:     Apr 14, 2010
              Total Posts:     17
              Total Questions:     5 (5 unresolved)

              why do you waste time here when you never get answers to any of your questions?
              Why do you waste your time here then continually criticizing posters and ignoring their problems?
              • 4. Re: 11.2.0.3 on OEL Linux - are huge pages finally compatible with AMM?
                Catch-22
                Kernel Hugepages and Posix shared memory are not compatible and mutually exclusive. The benefit of Hugepages stems from a larger page allocation size and guarantee that this memory, unlike Posix shared memory, will not be swapped to disk. Hugepages are reserved at system startup. From what I understand, you will still have to configure your Database startup parameter to either use AMM (/dev/shm) or ASMM to use kernel hugepages. The change introduces a fail-over to utilize additional regular memory for Oracle SGA in case the amount of available Hugepages is insufficient.
                • 5. Re: 11.2.0.3 on OEL Linux - are huge pages finally compatible with AMM?
                  user5749629
                  well... when you are tasked with building a VLDW on a modest budget - the options are few and the challenges are many. Very few things work or scale as advertised. But if you ask enough people - every once in a while a kind colleague shares a crumb that moves you a couple of steps forward.
                  • 6. Re: 11.2.0.3 on OEL Linux - are huge pages finally compatible with AMM?
                    Catch-22
                    Forum members are not obliged to provide feedback, but to mark questions as answered and give credit to helpful replies will avoid such issues.