Oracle shared memory parameters for UNIX/Linux Oracle Database Tips by Donald Burleson

Oracle MOSC Note 15566.1 Unix Semaphores and Shared Memory Explained, has a great summary of Oracle kernel related UNIX/Linux parameters:

System Parameters

=================

SHMMAX - kernel parameter controlling maximum size of one shared memory

         segment

SHMMHI - kernel parameter controlling maximum number of shared memory segments

         in the system

SHMSEG - kernel parameter controlling maximum number of shared memory segments

         a process can attach

SEMMNS - kernel parameter controlling maximum number of semphores in

         the system

SEMMNI - kernel parameter controlling maximum number of semaphore

         sets.  Semphores in Unix are allocated in sets of 1 to SEMMSL.

SEMMSL - kernel parameter controlling maximum number of semaphores in a

         semphore set.

SHMLBA - kernel parameter controlling alignment of shared memory

         segments; all segments must be attached at multiples of this value.

         Typically, non-tunable.

Oracle UNIX/Linux parameters:

SS_SEG_MAX - Oracle parameter specified at compile time (therefore,

             unmodifiable without an Oracle patch) which defines maximum

             number of segements the SGA can reside in.  Normally set to 20.

SS_SEM_MAX - Oracle parameter specified at compile time (therefore,

             unmodifiable without an Oracle patch) which defined maximum

             number of semaphore sets oracle will allocate.  Normally set to 10.

        Recommended Semaphore and Shared Memory Parameters 

Operating System        Shared Memory Parameters                 Semaphore 

----------------        ------------------------                 --------- 

Sun OS                  SHMSIZE = 32768                          SEMMNS = 200 

                        SHMMNI = 50                              SEMMNI = 50 

Solaris                 SHMMAX = 8388608(or larger than max SGA) SEMMNS = 200 

                        SHMSEG = 20                              SEMMSL = 50 

                        SHMMNI = 100                             SEMMNI = 70 

HP/UX                   SHMMAX = 0x4000000 (64 Mb)               SEMMNS = 128 

                        SHMSEG = 12                              SEMMNI = 10 

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