Slow WUA (Windows Update API)

Question

I'm working on a PowerShell script to do some Windows Update tasks. Most tasks center around getting a collection of Windows Updates that have not yet been applied, using the code snippet below. Once that collection is returned, I iterate through it and perform such tasks as hiding, downloading, or installing the updates.

I notice that this code can take anywhere from 6 to 115 sceconds to run. Typically the longer runs are after the machine has restarted or been idle for more than 15 minutes.

But if I open the Windows Update control panel item, it instantly knows how many updates are outstanding, and can give me a list (collection) of those outstanding updates. If I click WU's "check for updates" link, it will take >10 seconds to check again, and sometimes that check will yield different results than it "knew" instantly when I opened it.

So I assume that WUA maintains a cached collection of updates somewhere, probably updated automatically once daily. My question: how can my code access that cache, rather than running the longer "check for updates" code shown below? Specifically, I am hoping to quickly obtain an IUpdateCollection to work with.

$Session = New-Object -ComObject Microsoft.Update.Session            
$Searcher = $Session.CreateUpdateSearcher()
$Searcher.Online = $false  #tested $true and $false; $true slightly slower
$Criteria = "IsInstalled=0 and Type='Software'"
$SearchResult = $Searcher.Search($Criteria)           
$SearchResult.Updates 

Note that all this is happening on a current, Windows2012R2 system.

Answer 1

Look like the cache is a CAB file called wsusscn2.cab that is regularly downloaded from MSFT. There is a direct link to it in the msdn link I posted below. Perhaps write a script that downloads that once per day/week (maybe to a network share if this is going to be a widely deployed script), and then change your script to force it to always look at the CAB file instead of online. Like this:

$Session = New-Object -ComObject Microsoft.Update.Session       
$UServiceManager = New-Object -ComObject Microsoft.Update.ServiceManager
$UService =  $UServiceManager.AddScanPackageService("Offline Sync Service", "c:\wsusscn2.cab") 
$Searcher = $Session.CreateUpdateSearcher()
$Searcher.ServerSelection = 3  
$Searcher.ServiceID = $UService.ServiceID
$Criteria = "IsInstalled=0 and Type='Software'"
$SearchResult = $Searcher.Search($Criteria)           
$SearchResult.Updates 

msdn