To troubleshoot memory performance in a VMware vSphere environment, you should monitor the memory performance very carefully. In this aspect, you should monitor the following counters:

• Average memory active: The memory estimated to be used, based on recently touched memory pages.
• Average memory swapped in or out: Virtual memory swapped to or from disk.
• Average memory swapped: Total amount of memory swapped out. This indicates a possibility (with an unknown likelihood) of poor performance in future.