CSR-PDOS: Fast, Consistent Distributed File Systems through Operating System Speculation

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This project is investigating how generic support for speculativeexecution in a commodity operating system can improve the performanceand consistency of remote data access. Rather than block applicationsduring a remote file system operation, the operating systemcheckpoints the state of the calling process, predicts the result ofthe remote operation, and speculatively resumes execution based uponthe predicted results. If the speculation proves correct, thecheckpoint is discarded; if the speculation is incorrect, the callingprocess is restored to the checkpoint and the operation retried. Theoperating system guarantees safe execution by preventing speculativeprocesses from externalizing output until the speculations upon whichthat output depends have proven correct. By tracking causaldependencies created through inter-process communication, theoperating system allows multiple processes to safely share speculativestate. In addition to file systems, this project is exploring uses ofspeculation in diverse areas, including cyber-foraging, remotedesktops, and software installation.The major impact of this project lies in improving the performance,consistency guarantees, and safety of current distributed filesystems. The project is developing speculative versions of NFS, AFSand other distributed file systems that perform substantially betterthan current versions of these file systems. At the same time, theseversions provide stronger consistency and safety guarantees toapplications. The software artifacts developed as part of thisproject, including a modifed version of Linux that supportsspeculation, are being released to the open-source community.Additionally, educational initiatives are helping train the nextgeneration of systems software developers.