Caching mechanisms in PowerShell Universal.

$Cache Scope vs Server-Level Cache: The $Cache scope differs from the server-level cache as it only resides in the execution environment of feature you are using. They are different and cannot be used to get the other one.

Server-Level Cache

PowerShell Universal provides the ability to use a server-level cache to store data that you use between APIs, Automation and Dashboards. You can configure cache item life times use the Set-PSUCache cmdlet in any PowerShell script you run in PowerShell Universal. You can also retrieve items from the cache using Get-PSUCache.

Some examples of usages for the cache may be:

  • Collecting data with a scheduled job and displaying it within a dashboard

  • Collecting data from an API and using it in a job

  • Collecting using input from a dashboard and queuing it to run in a scheduled job

Setting items in the cache

To set items in the cache, you can use Set-PSUCache. Items in the cache are serialized to strings using CLIXML and the PowerShell serializer. When you retrieve objects from the cache, they will no longer be live objects.

Set-PSUCache -Key "CurrentDate" -Value (Get-Date)

There are three types of cache invalidation techniques you can employ.

Absolute Expiration

The AbsoluteExpiration parameter defines at what time the item in the cache is invalidated.

The follow example invalidates the cache item after 10 minutes.

Set-PSUCache -Key "CurrentDate" -Value (Get-Date) -AbsoluteExpiration (Get-Date).AddMinutes(10)

Absolute Expiration From Now

The AbsoluteExpirationFromNow parameter defines when a cache item is invalidated using a TimeSpan rather than a calculated DateTime.

The following cache item is invalidated 1 hour from now.

Set-PSUCache -Key "CurrentDate" -Value (Get-Date) -AbsoluteExpirationFromNow ([TimeSpan]::FromHours(1))

Sliding Expiration

The SlidingExpiration parameter allows you to defines the amount of time before the cache item is invalidated. Each time the cache item is accessed, the timer is reset.

The following cache item will be invalidated in 5 minutes. If it's accessed within those 5 minutes, it will be reset for another 5 minutes.

Set-PSUCache -Key "CurrentDate" -Value (Get-Date) -SlidingExpiration ([TimeSpan]::FromMinutes(5))

Getting items from the cache

You can use the Get-PSUCache cmdlet to retrieve items from the cache. You simply need to supply the key of the item you wish to retrieve. The deserialized object will be returned from the cmdlet.

Get-PSUCache -Key "CurrentDate"

$Cache Scope

APIs, Automation scripts and Dashboards all support a $Cache scope. This scope is used to cache data across runspaces that will persist in memory of each of the execution environments.

For example, if you set a $Cache variable in a dashboard, then it will not be available in an API. This is not true when using the Integrated environment. If a dashboard and API both use the integrated environment, then they share the cache scope.

You can set and retrieve data from the cache scope using variable assignment and retrieval syntax.

$Cache:MyValue = "Hello"
Write-Host $Cache:MyValue


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