Scenario: Persisted Cache

Synopsis

A strategic guide to implementing the persisted cache feature.

Description

The configuration system can be used to manage data caches. It offers a simple abstraction to handle import/export of cached settings. It also offers access to that cache across the entire process, irrespective of scope or runspace.

Strengths

• Automatic path management
• Can integrate caches provided from multiple locations into a single, coherent picture.
• Runspace-Unaware - a dedicated background runspace could maintain live data, while consuming runspaces could read from it.

Weaknesses

• Requires managing write conflicts in runspaced scenarios.

Implementation

The implementation consists of four basic steps:

• Initializing cached settings
• Importing cached data
• Using configuration settings
• Exporting updated cached data

Example

# Initializing settings
Set-PSFConfig -Module MyModule -Name Example1 -Value 42 -Validation integer -Initialize -Description "Some arbitrary example setting that will not be part of the cache"
Set-PSFConfig -Module MyModule -Name Example2 -Value $true -Validation bool -Initialize -Description "Some arbitrary example setting that will not be part of the cache"

Set-PSFConfig -Module MyModule -Name Example3 -Value @() -ModuleExport -Hidden -Initialize -Description "Some arbitrary example setting that WILL be part of the cache"
Set-PSFConfig -Module MyModule -Name Example4 -Value @() -ModuleExport -Hidden -Initialize -Description "Some arbitrary example setting that WILL be part of the cache"
Set-PSFConfig -Module MyModule -Name Example5 -Value @() -ModuleExport -Hidden -Initialize -Description "Some arbitrary example setting that WILL be part of the cache"

# Importing existing cache
Import-PSFConfig -ModuleName MyModule

# Access cache value in code
Get-PSFConfigValue -FullName MyModule.Example3

# (later)Exporting the current in-memory settings marked for cache-persistence
Export-PSFConfig -ModuleName MyModule

Resources

• It is recommended, to set cached settings to -Hidden, hiding them from random user access.
• The cache mechanism is handled more fully in the guide Persistence: Module Cache.
• The initialization process is an intricate event affecting most scenarios.

It’s a runspace world

Using the cache in a runspaced scenario generally risks conflict, since each import in each runspace overwrites the current cache values with the persisted ones. There are two basic ways to handle this:

• Always update the persisted cache using Export-PSFConfig immediately after the in-memory version is changed. This is easier to implement and minimizes the risk of collision.
• Make cache updates / persistence the task of a dedicated runspace. The PSFramework contains two solutions to implement dedicated runspace mechanisms: Managed Runspaces (Solution documentation pending, uses the commands Get-PSFRunspace, Register-PSFRunspace, Start-PSFRunspace and Stop-PSFRunspace) and Scheduled PowerShell Tasks (Solution Documentation pending, uses the commands Disable-PSFTaskEngineTask, Enable-PSFTaskEngineTask, Get-PSFTaskEngineTask, Register-PSFTaskEngineTask and Test-PSFTaskEngineTask).

Notes

Back to Configuration

Version	1.0
Written on:	2018-05-24
Updated on:	2018-06-07