| 摘要 |
Described is maintaining cached hash values for files in association with state data for each file that represents the state of that file's contents at the time of hashing. For example, in a journaling file system, the state data may comprise the update sequence number of the file in the journal and a journal identifier for that journal instance. A request for a hash value for a file is processed by determining whether a cached hash value is maintained for that file. If so, and the associated maintained state data matches current state data for the file, the file contents are unchanged since the last hash computation, whereby the cached hash value is returned in response to the request. Otherwise, a new hash value is computed for the file and returned, and cached for future use. Multiple types of hashes may be cached for a given file.
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