Compare hostnames and leases between CSV and DHCP info

Question

I have 3 nested loops and they do the following:

1. Get scopes from DHCP
2. Get hostnames from csv file
3. Compares hostnames and leases, matches are added to a hash table

There are 5 DHCP servers, 100's of scopes and thousands of leases.

What would be a good method to speed this up?

$DHServers = Get-DhcpServerInDC #get DHCP info
$hashtable = @{} #create hash table
foreach ($server in $DHServers){
$scopes = Get-DHCPServerv4Scope -ComputerName $server.dnsname #get all scopes in DHCP 
 
 foreach ($_ in (Import-Csv C:\script\Asset_List.csv | Select-Object -ExpandProperty asset)){ #get hostnames from list 
 
 foreach ($scope in $scopes){ 
 if($scope | Get-DhcpServerV4Lease -ComputerName $server.dnsname | Where-Object HostName -like "$_*" ){ #compares the hostname to find which lease it is in
 $scopename=$scope.name #matches give scope name
 $hashtable[$_] = $scopename #when a match is found, add keys and values to table
 } 
 }
 }
} 
 
 

• Sᴀᴍ Onᴇᴌᴀ: Welcome to Code Review! I changed the title so that it describes what the code does per site goals: "State what your code does in your title, not your main concerns about it.". Feel free to edit and give it a different title if there is something more appropriate.
• JosefZ: Why do you Import-Csv inside the foreach ($server in $DHServers) loop? Do it once and save to a variable Before the loop. File manipulation is always time consuming... Moreover, the foreach ($_ in ... seems to be a nonstandard construct, see difference between foreach and Foreach-Object. Read entire about_foreach topic.
• feelsgood: Doing it inside vs outside only took a few milliseconds off. Its calling DHCP info each time I loop that is the real problem.

Answer 1

Piping the DHCP calls through foreach-object instead and then comparing at the end, cut the time down from 3min to 1min. Everything I have read made it seem like foreach was faster. Having DHCP being processed down the pipe with foreach-object instead of several iterations with foreach makes foreach-objects more efficient.

$servers = Get-DHCPServerInDC
$hashtable = @{}
# scopes into the leases to go into the PsCustomObject to be matched later
$leases = $servers | ForEach-Object {
 $server = $_.dnsname
 Get-DHCPServerv4Scope -computerName $server #get scopes on DHCP serves
 
 } | ForEach-Object {
 $scope = $_
 $_ | Get-DHCPServerV4Lease -ComputerName $server | #get leases in all the scopes
 
 ForEach-Object {
 [pscustomobject]@{ # Make object to match later
 ScopeName = $scope.name #want name of scope only
 HostName = $_.hostname #want hostname of leases
 }
 }
}
$assets = (Import-CSV c:\script\Asset_List.csv).asset #pull asset list
 
$assets | ForEach-Object { $asset = $_ #Go through hostnames finding matching lease
 $leases | Where-Object { #check leases
 $_.HostName -like "${asset}*" #find hostname 
 } | ForEach-Object {
 $hashtable[$asset] = $_.ScopeName #store matches
 }
}
```