AIX V5.3 initial tuning recommendations
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AIX V5.3 initial tuning
The vast majority of AIX kernel tuning parameters are set appropriately by the AIX installation process. There are, however, a few tuning parameters which should be changed from the default values as soon as AIX is installed.
Tuning changes should be generally be made only with a specific objective in mind and in reaction to a performance issue which it seems likely that AIX kernel tuning can address. The changes recommended here are an exception to that general rule.
The settings of the parameters discussed below can be changed with the vmo
command. When making these (and most) tuning changes, the best practice is to use the -p flag on the vmo command, which causes tuning parameters to be changed on the running AIX image and configures AIX so that parameters will be set as specified each time AIX boots.
 | lru_file_repage
The AIX lru_file_repage kernel tuning parameter was introduced in AIX V5.2 ML5 and AIX V5.3 ML2. The default setting for lru_file_repage is 1 (on).
Before lru_file_repage was introduced, it was often necessary to alter minperm and maxperm/maxclient to get good performance, particularly when running an Oracle RDBMS workload. Now that lru_file_repage is available, when installing AIX V5.3 at ML5 and above it is best to leave minperm, maxperm, and maxclient at their default values and set lru_file_repage=0 (off). Subsequent AIX performance monitoring and analysis may suggest changing other vmo parameters, but it is best to start with minperm, maxperm, and maxclient at their default values unless other AIX V5.3 initial tuning recommendations come from some authoritative source. (The VMM Tuning Tip: Protecting Computational Memory article cited on the Performance Monitoring Documentation web page suggests setting minperm=5, maxperm=90, and maxclient=90 when setting lru_file_repage=0.) Use the AIX command vmo -a to display the settings of all vmo parameters and use vmo -L | awk '/^n\/a/{exit} {if ($2 != $3 && $2 != "n/a") {print $0} }' to display the settings of all vmo parameters which are set to a value other than the default.
See the Overview of AIX page replacement article on the IBM developerWorks web site for more information regarding lru_file_repage and instructions for changing it using the vmo command. |
Once initial tuning changes have been implemented, remember that tuning of any operating system (including AIX) is an interative process. That is, performance requirements should be identified, current performance should be assessed and, if appropriate, a small set of changes should be made. The effects of those changes should be assessed to determine if the changes caused any improvement. Changes which don't result in an improvement should generally be backed out. Changes which do result in an improvement should be preserved as the basis for further tuning. For more information, see The performance-tuning process article in the AIX V5.3 Performance management manual. Please note that it is often necessary to change AIX tuning in tandem with other tuning (eg, Oracle RDBMS memory use tuning).
