Feb 28, 2008

AIX - Tuning process memory size limits

When a process runs out of memory, the process often ends. On AIX systems, the system error log might indicate that the process ended due to memory allocation failure. Use the following command to display the error log

errpt -a | more

On UNIX systems, each user can either inherit resource limits from the root user or have specific limits defined. The most useful setting to use for the process size limits is unlimited. That way, the system process size limits are defined to allow the maximum process growth.

On AIX systems, the number of data segments that a process is allowed to use also limits the process memory size. The default number of data segments is 1. The size of a data segment is 256 MB. Data segments are shared for both data and stack. The maximum number of data segments a process can use is 8

On AIX, the number of segments that a process can use for data is controlled by the LDR_CNTRL environment variable. It is defined in the parent process of the process that is to be affected. For example, the following example defines one additional data segment:

export LDR_CNTRL=MAXDATA=0x10000000

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