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Semaphores
- Thread starter aixguy
- Start date
Aix is not like other operating systems. I believe AIX handles the semaphores for you.
You don't need to change anything on AIX. The limits are very high and rarely does an application run up against them. On AIX,they are by default acceptably high.
For details on the limits, see the following man pages: shmat(2),
semget(2) and msgget(2).
fileset for streams: bos.rte.streams
.... see the following documents.
Shared memory segments
On some UNIX systems, users edit /etc/master and set their own limits for IPC mechanisms (semaphore,
shared memory segments, and message queues). The problem with this method is that the higher the limits are
set, the bigger the kernel gets, and performance can be adversely affected. AIX uses a different method.
In AIX, upper limits are set for IPC mechanisms, and the individual IPC types are dynamically allocated and
deallocated up to these upper limits. These are not configurable in AIX.
Therefore, the kernel grows and shrinks in size as IPC types are allocated, so any performance hit lasts only for
the life of the IPC type.
This difference in methods sometimes confuses users who are installing or using databases. In AIX, IPC limits
are handled for users. The limit that may cause a problem is the maximum number of shared memory segments
per process (10).
The structures containing IPC limits are defined in three files in /usr/include/sys/: sem.h, msg.h, and shm.h.
The structures themselves are called seminfo, msginfo and shminfo, respectively. Only the
structures are defined--not the contents.
There is also a redbook that is great at tuning Oracle
Database Performance on AIX in DB2 UDB and
Oracle Environments, SG24-5511-00
Good Luck......
#-)
You don't need to change anything on AIX. The limits are very high and rarely does an application run up against them. On AIX,they are by default acceptably high.
For details on the limits, see the following man pages: shmat(2),
semget(2) and msgget(2).
fileset for streams: bos.rte.streams
.... see the following documents.
Shared memory segments
On some UNIX systems, users edit /etc/master and set their own limits for IPC mechanisms (semaphore,
shared memory segments, and message queues). The problem with this method is that the higher the limits are
set, the bigger the kernel gets, and performance can be adversely affected. AIX uses a different method.
In AIX, upper limits are set for IPC mechanisms, and the individual IPC types are dynamically allocated and
deallocated up to these upper limits. These are not configurable in AIX.
Therefore, the kernel grows and shrinks in size as IPC types are allocated, so any performance hit lasts only for
the life of the IPC type.
This difference in methods sometimes confuses users who are installing or using databases. In AIX, IPC limits
are handled for users. The limit that may cause a problem is the maximum number of shared memory segments
per process (10).
The structures containing IPC limits are defined in three files in /usr/include/sys/: sem.h, msg.h, and shm.h.
The structures themselves are called seminfo, msginfo and shminfo, respectively. Only the
structures are defined--not the contents.
There is also a redbook that is great at tuning Oracle
Database Performance on AIX in DB2 UDB and
Oracle Environments, SG24-5511-00
Good Luck......
#-)
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