Common Misconfigured HP-UX Resources (April 2006)

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Semaphore undo table
semmnu
24 bytes + (8*semume)
256 (semmnu)
100 (semume)
Changes in HP-UX 11i v2
Beginning with the HP-UX 11i v2, the dynamic changes described in the previous section define the
default behavior; therefore, no patch is necessary. The sema tunable has been obsoleted. The sizes
of the data structures remain the same, so all of the formulas for calculating the kernel boot size
remain the same. Keep in mind that the semaphores themselves (limited by semmns) are allocated as
needed and will not consume space at boot time. Thus, memory usage will grow and shrink as
semaphores are allocated and freed. The other data structures are still allocated at boot time;
therefore, you must be careful when changing semmnu and semume. One last change is that the limit
on the total number of semaphores in the system has been enlarged. The new limit is 335,534,080,
as described on the manpage.
Guidelines for Configuring Semaphores
Many third-party applications make heavy use of the Sys V IPC semaphore mechanism available
within HP-UX. Understanding all of the tunables, what they represent, and how changing them can
affect the memory consumed by your kernel is important so that you do not mistakenly tune the
semaphores too high, leaving too little memory to accomplish other important tasks.
One of the most common mistakes is the setting of the semaphore undo table. Remember that there is
a multiplicative effect from setting semmnu and semume.
Also, if you manage multiple systems, be sure that the semaphore tables are scaled appropriately
given the memory size of each. A given set of tunables may work great on a system with 8 GB of
memory, but have severe memory implications on a system with only 1 GB of memory.