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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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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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