When a user logs on to the SAP NetWeaver Application Server (AS) Java, the user management engine (UME) reads the user's group and role assignments:
From this information, the UME creates a list of UMEactions and determines the permissions assigned to the user. The UME stores this information in a cache on the node where the user is logged in.
Permissions of a User Stored in the User Cache
Another example of a use of the UME cache is when an administrator looks for all the members of a group, the UMErecords information about the group and its members in the UMEcache on the server.
The UME refreshes this cache whenever you change group or role assignments. By default, the UMErefreshes the cache automatically after the user has been logged in for about an hour.
The cache uses the initial cache size to keep the cache current. The initial cache size is configurable. By default the UME is configured to cache the information for up to 5000 objects. In actual operation, the number of objects cached can exceed the configured value temporarily. When the number of objects in the cache exceeds the initial cache size, the cache marks selected objects as candidates for deletion. When the garbage collector runs, it evaluates the entries and removes objects until the cache is down to the required size. Objects remain in the cache until the garbage collector removes them or you restart the server. You can also manually trigger a cache refresh.