Upgrade-SPContentDatabase in parallel as part of CU upgrade

Question

I am updating our 2013 environments to the October 2020 CU to patch a vulnerability reported by our security team. The last time we patched CUs in the production environment, the Upgrade-SPContent database portion took a really long time. We have 80+ content databases in one web application and about 60 in the other, so we wanted to split the load across several servers to decrease the upgrade time.

To remedy that, we updated our documentation to run the Upgrade command in parallel on up to 4 servers. The script I was planning on using is below, but I'm wondering if it will work as I expect it to across multiple servers. I'm trying to avoid hard coding database names into the script to make it easier to open and run on multiple servers.

Add-PSSnapin Microsoft.SharePOint.Powershell
$webapp = get-spwebapplication | Where-Object {$_.Url -like "*hnsc01*"} 
$collabs = Get-SPContentDatabase -WebApplication $webapp | Where-Object {$_.NeedsUpgrade -eq $true} | Sort-Object Name 

foreach($db in $collabs){
    Write-Host $("Upgrading content database: {0}" -f $db.Name) -ForegroundColor Yellow
    Upgrade-SPContentDatabase -Identity $db.Id -Confirm:$false 
}

My concern is that it will work fine on one server, but start to fail constantly on other servers as the initial Get-SPContentDatabase call "caches" the result in a point in time. I might be able to get around that by putting a second call in the foreach loop to check again if it needs updated.

Edit to include an updated script based on comments to make sure I'm understanding correctly:

$webapps = Get-SPWebApplication
foreach($webapp in $webapps){ 
    $dbs = Get-SPContentDatabase -WebApplication $webapp | Where-Object {$_.NeedsUpgrade -eq $true} | Sort-Object Name 
    foreach($db in $dbs){
        Write-Host $("Creating job to upgrade content database: {0}" -f $db.Name) -ForegroundColor Yellow
        Start-Job -Name $db.Name -ScriptBlock {Upgrade-SPContentDatabase -Identity $db.Id -Confirm:$false}
    }
}

Answer 1

The issue isn't originating from the server the script is running on (the SharePoint server), but rather the time it takes to update the schema on the SQL server and the SQL server load.

If you want to parallel upgrades, use Start-Job instead of a foreach which will serialize the upgrades.