Sp eculative state is never externally visible in

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Unformatted text preview: fork, exit, signals, pip es, fifos, Unix sockets, and files in local and distributed file systems. All other forms of IPC currently block the sp eculative process until the sp eculations on which it dep ends are resolved. Since sp eculation is implemented entirely in the op erating system, no application modification is required. Sp eculative state is never externally visible. In other words, the semantics of the sp eculative version of a file system are identical to the semantics of the non-sp eculative version; however, the p erformance of the sp eculative version is b etter. Results from PostMark and Andrew-style b enchmarks show that Sp eculator improves the p erformance of NFS by more than a factor of 2 over local-area networks; over networks with 30 ms of round-trip latency, sp eculation makes NFS more than 14 times faster. We have also created a version of the Blue File System [24] that uses Sp eculator to provide single-copy semantics, in which the file consistency seen by two processes sharing a file and running on two different file clients is identical to the consistency that they would see if they were running on the same client. In • commit_speculation || fail_speculation • create_speculation: – Create copy-on-write fork of current process, save it away (don’t run it) – On commit_speculation: Delete copy – On fail: Replace or...
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