Powershell-connector

How many properties are in your result for each User?

You can try to increase the reload threshold as described here.

https://support.oneidentity.com/technical-documents/identity-manager/9.1/target-system-synchronization-reference-guide/41#TOPIC-1868903

Both Get-Users and Get-User returns 11 properties. I've now increased the threshold to 12.

But is this the excpected behaviour, fetching all users and then fetching them one by one? Seems stupid to me..

The Get-Users cmdlet should only retrieve the key, revision, and display properties. The Get-User retrieves all properties. In your case where the slim list retrieval returns all properties it makes sense to cache the list if memory availability allows. The Get-User cmdlet will index into the cached list taking away the network calls and bad performance. If you do not have enough memory to cache the list you should only retrieve the slim list and depend on the revision counter to reduce the synchronization duration when the revision counters are fully built. 

The Get-Users cmdlet should only retrieve the key, revision, and display properties. The Get-User retrieves all properties. In your case where the slim list retrieval returns all properties it makes sense to cache the list if memory availability allows. The Get-User cmdlet will index into the cached list taking away the network calls and bad performance. If you do not have enough memory to cache the list you should only retrieve the slim list and depend on the revision counter to reduce the synchronization duration when the revision counters are fully built. 

Any suggestion how to make Get-User index into the cached list?

function Get-Accounts() {
	if (-not $Global:Accounts) {
    		$Global:Accounts = Invoke-Restmethod https://app1/getusers
	}
	$Global:Accounts
}

function Get-Account($id) {
	if ($Global:Accounts) {
        $account = New-Object PSCustomObject -Property $global:Accounts[$id]
    else {
        $account = Invoke-Restmethod https://app1/getusers/$id
    }
    $account
}

 <ReadConfiguration>
                <ListingCommand Command="Get-Accounts"/>
                <CommandSequence>
                    <Item Command="Get-Account" Order="1"/>
                </CommandSequence>
</ReadConfiguration>