Kernel Tuning for Oracle on Unix - EcoSys - Help - Hexagon

EcoSys Performance Tuning

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Recommendations for IBM AIX Kernel Parameters

lru_file_repage = 0

maxclient% = 90

minperm% = 5

page_steal_method = 1

The page_steal_method parameter was introduced in APAR IY59704 in AIX V5.3 ML01. The parameter is available in all AIX V5.3 levels above ML01. Setting page_steal_method = 1 is helpful when file cache occupies only a small percentage of memory.

Recommendations for HP-UX Kernel Parameters

  • SEMMSL - The maximum number of semaphores that can be in one semaphore set. It should be same size as maximum number of Oracle processes

  • SEMMNS - Set to the sum of the PROCESSES parameter for each Oracle database plus two times the largest PROCESSES value, plus 10 times the number of Oracle databases

  • SHMMAX - Maximum size of a shared memory segment. Adjust to maximum required (> MAX(SGA, EM)

Using Asynchronous I/O

To improve I/O performance on character or raw block devices, enable asynchronous I/O. The result is less I/O overhead and higher output.


Using the System Management Interface Tool (SMIT), enable asynchronous I/O by adjusting the kernel parameters.

The kernel database processes (aioserver) control each request from the time a request is taken off the queue to the time it is completed. The number of aioserver servers determines the number of AIO requests that can be processed in the system concurrently. So, it is important to tune the number of aioserver processes when using file systems to store Oracle Database data files. Refer to your AIX Administration guide for more details.


To permit the Oracle Database to process asynchronous I/O operations, the OSDBA group (dba) must have the MLOCK privilege. You must use the System Administrator Management (SAM) utility to configure the asynchronous disk driver into the HP-UX kernel. For more information, refer to your HP-UX Administration guide for more detail.