Method and apparatus for shadowing a hierarchical file system index structure to enable error recovery

Abstract

The method of the invention updates a tree arranged index for an hierarchical file system (HFS). The index includes at least one index value, i.e., an index page, that is logically positioned between an index anchor value and a sequence page. The sequence page includes actual index data. Logical positioning of the index page is determined by one or more pointers. The method initially responds to an index update request by making an update “shadow” copy of (i) a sequence page and (ii) any other index pages, up to and including a root page, that are to be updated in accord with the update request. Thereafter, an index manager updates the shadow copy of the sequence page in accord with the update request. The index manager further updates the root page and each shadowed index page that is present in a path to the updated sequence page to indicate that the path has been updated and includes the most current data. If a cancel or error indication occurs prior to updating of the index path, the shadowed copies of the sequence page, index page and root page are released, enabling the system to return to the non-updated pages. Otherwise, the index manager updates the index anchor value to point to the updated root page, thereby indicating that the index update has been successfully accomplished. Periodically, the new index anchor value, sequence page, index and root pages are written to disk.

Dependencies are inferred from the claim text.