How Memory Usage is Calculated

Processes have private memory, which is owned privately by each process, and they have shared memory. Shared memory can be shared (in theory) with none, one, some, or all other processes on the same system.

In Application Discovery memory calculations are made for matched applications and displayed in the detail screen of a host (total memory usage and by application), as shown in the following image.

Memory columns
showing total and by application memory usage

In Application Discovery, application memory shown is the sum of all private memory in use by all the processes in that application and the sum of all shared memory in use by all the processes in that application. That is, shared memory is displayed as though it is not shared. This means that the totals shown for memory usage are an overstated approximation of actual memory usage for any particular application.

Here is why accurately summing memory shared among processes is difficult to do:

The degree of sharing among processes is unknown. For a given process, the shared memory can be shared with every process on the system, only some processes on the system, only some processes within the application, or with all of the processes within the application.
The 'right' answer for how to sum shared memory for processes depends in part on how the individual administrator uses the information for planning. For example, is the administrator thinking of adding an application instance to the host? Is he or she thinking of moving an application instance to another host? Is the administrator thinking of moving the entire application to another host?

To arrive at a usable deterministic answer, all the shared memory for each process is summed. This conservative calculation should allow you to safely estimate resource usage for the applications shown.

How Memory Usage is Calculated

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