InterSystems: The power behind what matters   
Class Reference   

Extent Management
For classes that use the default storage class (%Library.CacheStorage), Caché maintains extent definitions and globals that those extents have registered for use with its Extent Manager. The interface to the Extent Manager is through the %ExtentMgr.Util class. This registration process occurs during class compilation. If there are any errors or name conflicts, these cause the compile to fail. For compilation to succeed, resolve the conflicts; this usually involves either changing the name of the index or adding explicit storage locations for the data.
The MANAGEDEXTENT class parameter has a default value of 1; this value causes global name registration and a conflicting use check. A value of 0 specifies that there is neither registration nor conflict checking.
If an application has multiple classes intentionally sharing a global reference, specify that MANAGEDEXTENT equals 0 for all the relevant classes, if they use default storage. Otherwise, recompilation will generate the error such as
ERROR #5564: Storage reference: '^This.App.Global used in 'User.ClassA.cls' 
is already registered for use by 'User.ClassB.cls'
To delete extent metadata, there are multiple approaches: