Symptoms
When performing audit or redesign of your SharePoint infrastructure it may be necessary to delete some of the old site collections. You may also discover that some of the sites were registered in K2 and probably that group providers were added for certain sub-sites which is not recommended. This leads to the following questions:
How to remove unnecessary group providers from K2? (e.g. related with deleted sites)
Is it the case thar addition of group providers for sub-sites is not recommended? Can those be deleted without any issues as there are running processes/workflows, as long as the site collection has been registered?
Diagnoses
At the moment there is no OOTB/GUI way to delete unused group providers but there is an existing feature request to add such functionality (TFS 169451) which will allow to perform deletion from UI and will also clean Identity Service tables to remove all entries for this provider.
Note that K2 KB KB001257 "Important considerations when registering a SharePoint Group Provider in K2" says that "Once a SharePoint Group Provider label has been created for the site collection it should never be changed or removed."
The reason why it says so is because if the group from this group provider was used at some point in a process, there is no easy way to detect this dependency and if a process is dependent on this group and you delete group provider, your instances will go into error state.
But in case you are sure that groups from this group provider are not used in any active processes and more over site itself is already deleted you may need to delete it.
The only way for is to manually remove this provider from the database. Please log a ticket with K2 support for this to get guidance on this process.
As for creating group providers for sub-sites indeed it is not recommended approach as you may run into the issues of having duplicate security providers. As per K2 documentation: "Security Provider labels should always be unique – unique per provider, unique per SharePoint site." You have to create group provider on a site collection level because the users are all ‘known’ on the site collection level not specifically to the sub-site.
See also: K2 KB KB001257 "Important considerations when registering a SharePoint Group Provider in K2"
Resolution
See Diagnosis section. In case you need to delete SP group provider please log a ticket with K2 support to get an assistance with deleting it from DB.
