Consultor Eletrônico

Status: Verified

GOAL:

Suggeston for tuning the AIX virtual memory in certain conditions.

GOAL:

What is the proper use of the vmtune command on all IBM AIX Progress Database servers.

FACT(s) (Environment):

IBM AIX POWER 5.1
IBM AIX 4.3.3
IBM AIX 4.3

FIX:

When running an AIX system and using 50% or more of the RAM on that system for Progress shared memory - i.e: one or more databases with large databaseblocks (-B) settings; benefits may be gained from the following setting for vmtune:
vmtune -p 5 -P 6
Where:
minperm (-p): Specifies the point below which file pages are protected from the repage algorithm. This value is a percentage of the total real-memory page frames in the system. The specified value must be greater than or equal to 5.
maxperm (-P): Specifies the point above which the page stealing algorithm steals only file pages. This value is expressed as a percentage of the total real-memory page frames in the system. The specified value must be greater than or equal to 5. These settings used in conjunction are meant to reduce the amount of excessive paging that might occur if using large amounts of RAM for Progress database servers.
The vmtune utility is part of the IBM AIX performance toolkit. It provides a programmatic interface to the vm_ctl(2) system call, and allows display and tuning of system-wide virtual-memory parameters.
If these settings are not tuned, excessive paging can occur when a large amount of I/O activity occurs (as seen in vmstat statistics). These recommended settings will minimize the memory usage for file I/O when higher -B or other Progress related parameters that may include extended memory and thereby requires that OS buffers are shrunk down to values described in above.
The idea is to minimize the paging of memory onto the disks. Each environment will need to be individually tuned in relation to it's requirements.