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Interpreting Memory Statistics on DataPower

In support we often get asked about the differences between the several memory statistics available on the DataPower Appliances. The 2 most common are the output from 'show load' vs. 'show memory'. (In this post I will refer to the CLI display; the same data is also available in the webGUI under Status->System->Memory Usage & Status->System->System Usage (also via SNMP, etc.))

You can see these 2 outputs here:

XI50(config)# show memory

  Memory Usage: 32 %  Total Memory: 4148536 kilobytes  Used Memory: 1337523 kilobytes  Free Memory: 2811013 kilobytes  Requested Memory: 2779472 kilobytes  Hold Memory: 1669093 kilobytes

XI50(config)# show load

  Task ID Task Name Load Work List CPU Memory File Count  ------- --------- ---- --------- --- ------ ----------        1      main    0         0   4     82        214        2      odbc    0         0   2      1         15        3      odbc    0         0   3      1         15       14       ssh    0         0   0      0         29

You can see there the calculation of Used/Free = Memory Usage.

The answer is actually fairly complex. The simplest explanation is that the 'load' metric includes memory that is cached; which the other does not.
The 'show load' includes cached memory as well as some other values. These are internal non-configurable memory caches to help optimize the performance of the device.

To summarize, support generally recommends to monitor the 'memory' metric most closely. That is the value on which the Throttler triggers and which best reflects the available capacity of the device.

Here are some good links for learning more about DataPower memory management:

• Managing WebSphere DataPower SOA Appliance configurations for high availability, consistency, and control, Part 1
• Resource management and analysis best practices for WebSphere DataPower
• Webcast replay: Troubleshooting IBM DataPower Appliances