PowerShell: calculate delta between successive values of the rawvalue property for each counter - powershell

Question

'evening,
I'm brand new at PowerShell scripting (and to this site) and need to write a script that:
gathers performance counters (in this case, TCP) several times
calculates the difference between successive values of the rawvalue property of each counter
Stipulating that every interval T the script iterates through the performance counters N times, and said performance counters are "A" and "B", and we're counting from 0, it needs to perform the following calculations:
A[1st] - A[0th],
A[2nd] - A[1st],
A[3rd] - A[2nd]
...
At present, the script only iterates through the counters, twice (i.e. N = 2 in this case). The goal is to be able to be able to iterate through these counters "many" (e.g. a couple hundred) times.
Currently the script reads the raw value of each counter into a single array. Here it is:
$cntr = (get-counter -listset tcpv4).paths
$arry = #()
for ($i=0; $i -lt 2; $i++) {
write-host "`nThis is iteration $i`n"
foreach ($elmt in $cntr) {
$z = (get-counter -counter $elmt).countersamples[0].rawvalue
$arry = $arry + $z
write-host "$elmt is: $z`n"
}
}
When I run this script, I get output just like the following:
This is iteration 0
\TCPv4\Segments/sec is: 24723
\TCPv4\Connections Established is: 27
\TCPv4\Connections Active is: 796
\TCPv4\Connections Passive is: 47
\TCPv4\Connection Failures is: 158
\TCPv4\Connections Reset is: 412
\TCPv4\Segments Received/sec is: 14902
\TCPv4\Segments Sent/sec is: 9822
\TCPv4\Segments Retransmitted/sec is: 199
This is iteration 1
\TCPv4\Segments/sec is: 24727
\TCPv4\Connections Established is: 27
\TCPv4\Connections Active is: 798
\TCPv4\Connections Passive is: 47
\TCPv4\Connection Failures is: 159
\TCPv4\Connections Reset is: 412
\TCPv4\Segments Received/sec is: 14903
\TCPv4\Segments Sent/sec is: 9824
\TCPv4\Segments Retransmitted/sec is: 200
e.g. The two values for the rawvalue property for the "\TCPv4\Segments Retransmitted/sec" counter are $arry[8] and $arry[17] respectively. To derive the difference between the two I'm using:
write-host "The difference between the successive counters for $($cntr[-1]) is $($($arry[17]) - $($arry[8]))."
Any help would be greatly appreciated.

Answer 1

I poked at it some, and this fell out:
$cntr = (get-counter -listset tcpv4).paths
$LastValue = #{}
Get-Counter $cntr -SampleInterval 2 -MaxSamples 5 |
foreach {
foreach ($Sample in $_.CounterSamples)
{
$ht = [Ordered]#{
Counter = $Sample.path.split('\')[-1]
TimeStamp = $_.TimeStamp
RawValue = $Sample.RawValue
LastValue = $LastValue[$Sample.Path]
Change = $Sample.RawValue - $LastValue[$Sample.Path]
}
if ($LastValue.ContainsKey($Sample.path))
{ [PSCustomObject]$ht }
$LastValue[$Sample.Path] = $Sample.RawValue
}
}
Edit:
This should work on V2:
$cntr = (get-counter -listset tcpv4).paths
$LastValue = #{}
Get-Counter $cntr -SampleInterval 10 -MaxSamples 3 |
foreach {
foreach ($Sample in $_.CounterSamples)
{
$Object = '' |
Select-Object Counter,TimeStamp,RawValue,LastValue,Change
$Object.Counter = $Sample.path.split('\')[-1]
$Object.TimeStamp = $_.TimeStamp
$Object.RawValue = $Sample.RawValue
$Object.LastValue = $LastValue[$Sample.Path]
$Object.Change = $Sample.RawValue - $LastValue[$Sample.Path]
if ($LastValue.ContainsKey($Sample.path))
{ $Object }
$LastValue[$Sample.Path] = $Sample.RawValue
}
}

Answer 2

Ok. Well lets work with this then
$cntr = (get-counter -listset tcpv4).paths
$arry = #()
$maximumIterations = 2 # Variable based since you intended to change this.
# Cycle the counters while recording the values. Once completed we will calculate change.
for ($i=1; $i -le $maximumIterations; $i++) {
foreach ($elmt in $cntr) {
$arry += New-Object -TypeName PsCustomObject -Property #{
Iteration = $i
Counter = $elmt
RawValue = (get-counter -counter $elmt).countersamples[0].rawvalue
Change = $null
}
}
}
# Now that we have all the values lets calculate the rate of change over each iteration.
$arry | Where-Object{$_.Iteration -gt 1} | ForEach-Object{
$previousIteration = $_.Iteration - 1
$thisCounter = $_.Counter
$thisValue = $_.RawValue
$previousValue = ($arry | Where-Object{$_.Counter -eq $thisCounter -and $_.Iteration -eq $previousIteration}).RawValue
$_.Change = $thisValue - $previousValue
}
$arry | Select Iteration,Counter,RawValue,Change
Not that we have to but I collected all of the counters data along with their iteration value like you were putting against Write-Host. You will notice that I create a placeholder for Change but do not populate it. Before the calculations $arry would have data like the following. Note: the output is truncated
Iteration Change Counter RawValue
--------- ------ ------- --------
1 \TCPv4\Segments/sec 28324837
1 \TCPv4\Connections Established 120
. .............................. .....
2 \TCPv4\Segments/sec 28325441
2 \TCPv4\Connections Established 125
Once all of that data is collected into $arry we get all the iterations that are not the first and process each item individually. Using the data of the current item in the pipeline we match it up with the previous iterations value. Using the same values as above we get the changes you were hoping to monitor
Iteration Counter RawValue Change
--------- ------- -------- ------
1 \TCPv4\Segments/sec 28324837
1 \TCPv4\Connections Established 120
. .............................. .....
2 \TCPv4\Segments/sec 28325441 604
2 \TCPv4\Connections Established 125 5