1. A method for determining authorization to operate on a file, the method comprising the computer-implemented steps of: receiving a request, associated with a session, for an operation on the file; looking in one or more session caches that are associated with said session for an entry that contains permissions metadata for said file; if said entry is not in said one or more session caches, then looking for said entry in one or more shared caches whose entries are accessible to multiple sessions; and if said entry is not in said one or more shared caches, then obtaining said permissions metadata from a source other than said one or more session caches and said one or more shared caches; and using said permission data to determine whether said operation may be performed on said file.