Memory Utilization - Am I seeing it right

While doing Performance testing, in addition to response times we need to understand how much OS-Resource our system consumes. OS-Resource might involve monitoring things like Memory,CPU and Network I/O. While working on a Multi-process or Multi-threaded applications and comparing memory consumption among them, it is very important to know how one calculates the memory.

               There are various ways to look at the memory of a process. Let’s look at a on-premise machine (Cent-OS) to look at the memory of a process

              

On using a “top” a linux based tool, I got the above memory snapshot for different “top” processes. So, which one should one consider for memory?

VIRT – virtual size of a process where it holds the memory within its process, memory shared with other processes and shared libraries.

RES – residential size of process which will accurately provide the physical size of the defined process (Code + Data)

SHR – Shared memory indicates the memory consumed by the shared libraries which are indicated in the virtual size of the process.

Now at a glance, If I need to understand the memory consumed by a process I would go  for the “Residential size”  of the process. Residential size actually gives us the accurate memory consumption of the process.

Now let’s say that you would like to monitor or look for “Core Memory” of a process. When running applications in Production, you might want to look at how much memory does the process itself takes (which does not include any memory of the shared libraries which might also be related to memory shared with other processes). So to calculate that you might need to look for the below formulae

                 

                    Core-Memory = RES – SHR.

  

The same kind of convention applies for windows too. There we call it as working set and private working set. You can configure your “task manager” to show which ever kind of memory(by default it shows private working set). If you wish to do it through script then you can use the windows API “WMIObject”.

Here’s a snippet

Get-WmiObject -class Win32_PerfFormattedData_PerfProc_Process | where{$_.idprocess -eq $processId} | select `

 @{Name="Process Id"; Expression = {$_.idprocess}},`

 @{Name="Counter Name"; Expression = {$_.name}},`

@{Name="CPU Usage"; Expression = {$_.PercentProcessorTime}},`

@{Name="Private Working Set"; Expression = {$_.workingSetPrivate / 1mb}}   

This should help you understand how much memory is your process used and which one adds significance