In a PowerShell Provider, when do you refresh vs cache data?

I am writing a PowerShell provider in C#. The provider exposes an applications domain objects through a drive-like interface. For example:

my:\Users\joe@blow.com
my:\Customers\Marty

This data ultimately comes from a database.

I have been unable to find any great guidance for when you should go to the database for data, and when you should cache it. I find that PowerShell calls methods like ItemExists and GetChildNames many times; often repeatedly for the same command. It is impractical to go to the database 5 or 6 times just because they hit Tab for auto-complete, for example.

But at the same time, as a user at the command prompt, if I type Get-ChildItem (dir) and see the list, then do something outside PowerShell so that I know the data is refreshed, taking another directory listing should expect to see any changes to the database.

I feel that if I knew the right term to describe my problem (in PowerShell parlance) I would be able to Google the answer or find an existing duplicate question, but I'm stuck.

This has very little to do with powershell and everything to do with your data, and how important it is to refresh it. A simple caching scheme would be to use a time based system whereby after N minutes, a request to your back end's data layer would pull a fresh copy and reset the timer. It seems you already have an idea what your particular rules should be. I don't think two successive "dir" commands should always result in two pulls from the backing store, but you do think so for your system. So make it so.

UPDATE

Perhaps a simple guiding principle might be that you should only refresh your data once per provider command issued. The list of built-in commands that operate on provider items consists of:

• Clear-Item
• Copy-Item
• Get-Item
• Invoke-Item
• Move-Item
• New-Item
• Remove-Item
• Rename-Item
• Set-Item

Additionally, the list of built-in commands that operate on provider item properties consists of:

• Clear-ItemProperty
• Copy-ItemProperty
• Get-ItemProperty
• Move-ItemProperty
• New-ItemProperty
• Remove-ItemProperty
• Rename-ItemProperty
• Set-ItemProperty

And finally, for reading/writing content, we use:

• Add-Content
• Clear-Content
• Get-Content
• Set-Content

Each of these commands has a corresponding method in NavigationCmdletProvider (for hierarchical datastores) and this is where you might want to refresh your data. When implementing the New/Move/Rename/Remove/Set/Clear and other data changing methods, you should use some kind of optimistic concurrency methodology as provider instances in PowerShell are not singletons; there may be one or more instances in play at any time.

I wrote a provider that takes its implementation from script that you may find easier to prototype things in. See http://psprovider.codeplex.com/

Hope this helps.