CSE 124 Lecture Notes - Lecture 10: Parsing, Local Procedure Call, Data Center
26 Apr 2018
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Hard state: do not lose data (required for correctness ) Write to disk, or cold remote backup. Exact replica or recoverable (db: checkpoint + op log) It is up to the clients to cache data. Read from server, caching in nfs client. Ensure ordering, but only between application close() and open(), not all writes() and reads()! If b opens after a closes, will see a"s writes. What if two clients open at the same time? no guarantees! Get file"s last modification time from server: getattr(fh) Both when first open file, then poll every 3-60 seconds. If last mod time changed, flush dirty blocks and invalidate cache. A mish-mash of old and new versions of the file! Server broadcasts notification to all clients if file changes. A client can request a lock over a file / byte range. Client thinks it has the lock, but server gives lock to another! Client obtains lease on file for read or write.
