Parameter Description
SEMMNS The number of semaphores in the system. In addition to the
requirements of the operating system and other software, you should
allow at least one semaphore for each Oracle server process—that is,
the sum of the setting of the PROCESSES parameter for all instances
on the system. If the semaphore clients are not always shut down and
started up in strict sequence, then an extra allowance at least equal to
the largest single requirement is recommended.
Further, the kernel parameter controlling the maximum number of
simultaneous processes owned by a single named user (often MAXUP)
should be at least equal to the SEMMNS setting, with an allowance for
other administrative processes owned by the "oracle" user that do not
require semaphores. However, this parameter should not be so large
as to allow the risk of another user creating so many processes that the
kernel process table would be completely filled. Therefore, the kernel
parameter controlling the maximum number of simultaneous
processes for all users (often NPROC) should be at least three times
the value of SEMMNS.
SEMMSL
The size limit for a single semaphore set. This parameter is not defined
on some operating systems. Where it is defined, and where Oracle
requires all the semaphores for an instance to be allocated in a single
semaphore set, this parameter must be at least equal to the largest
PROCESSES parameter required for any instance.
SEMMNI
The number of semaphore set identifiers in the system. In addition to
the requirements of the operating system and other software, you
should allow one identifier per instance, or more if the SEMMSL
parameter is set such that multiple semaphore sets will be required for
any instance.
SEMMNU
The number of semaphore undo structures in the system. Undo
structures are used to recover the kernel semaphore data structures in
the event of the unexpected death of a process during a semaphore
operation. SEMMNU should be greater than the peak number of
running and runnable processes.
If Oracle uses System V semaphores on your operating system by default, but also
supports the use of a post-wait driver, then you should use the post-wait driver
instead. This normally involves setting the USE_POST_WAIT_DRIVER
parameter to TRUE, and it is sometimes necessary to set the
POST_WAIT_DEVICE parameter as well. Please consult your Oracle installation
guide, because the instructions are operating system and release dependent.
The semaphore parameters are operating system kernel
parameters and cannot be set in the Oracle initialization
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