2 Replies Latest reply: Oct 20, 2011 7:43 PM by Catch~22 RSS

    SHMMAX kernel paramter for Oracle 11gR2 XE

    Catch~22
      According to the documentation at http://download.oracle.com/docs/cd/E17781_01/install.112/e18802/toc.htm#BABJFAIA Oracle 11gR2 Express Edition requires a kernel SHMMAX parameter of 4294967295, which is 4 GB - 1 byte.

      Oracle 11gR2 is limited to 1 GB of RAM according to http://download.oracle.com/docs/cd/E17781_01/install.112/e18802/toc.htm#BABHJHHC

      As far as I know, the kernel.shmmax parameter just sets the upper boundary of memory in bytes a process can allocate. It does not mean that it is going to use that memory, but what happens if there is a memory leak, or other software goes mad.

      As a safeguard for the OS, wouldn't it be more appropriate to set the SHMMAX size for Oracle 11gR2 XE to 1 GB or 1073741823 bytes? 32 MB is the default.

      Could the 4 GB setting be a relict from the 32-bit kernel days, defining the max. memory possible, actually 3 GB to be more precise?

      Thanks!
        • 1. Re: SHMMAX kernel paramter for Oracle 11gR2 XE
          Tommyreynolds-Oracle
          As far as I know, the kernel.shmmax parameter just sets the upper boundary of memory in bytes a process can allocate. It does not mean that it is going to use that memory, but what happens if there is a memory leak, or other software goes mad.

          As a safeguard for the OS, wouldn't it be more appropriate to set the SHMMAX size for Oracle 11gR2 XE to 1 GB or 1073741823 bytes? 32 MB is the default.
          Yes, the SHMMAX is mostly just a sanity check. It keeps a rogue application from allocating lots of shared memory and causing a denial of service (starvation) to other applications.

          While I would not dream of speaking for the RDBMS team, I suspect that is just a don't bother me kind of value: excessively generous, but an attempt to avoid a different class of problems. I'd keep on sizing the value appropriately for my SGA. No reason for the value to be much larger than your largest SGA's size.
          • 2. Re: SHMMAX kernel paramter for Oracle 11gR2 XE
            Catch~22
            That's what I thought. Thanks a lot for your confirmation. I consider your answer as being correct.