1 / 5

Slides by Prof. Jennifer Welch

Slides by Prof. Jennifer Welch. Consensus Problem. Every processor has an input. Termination: Eventually every nonfaulty processor must decide on a value. decision is irrevocable! Agreement: All decisions by nonfaulty processors must be the same.

vernados-karan
Télécharger la présentation

Slides by Prof. Jennifer Welch

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Set 9: Fault Tolerant Consensus Slides by Prof. Jennifer Welch

  2. Consensus Problem • Every processor has an input. • Termination: Eventually every nonfaulty processor must decide on a value. • decision is irrevocable! • Agreement: All decisions by nonfaulty processors must be the same. • Validity: If all inputs are the same, then the decision of a nonfaulty processor must equal the common input. Set 9: Fault Tolerant Consensus

  3. Agreement Condition • The agreement condition above requires “exact agreement” • The output must be exactly equal Set 9: Fault Tolerant Consensus

  4. FLP Impossibility Result • Fischer, Lynch, Paterson (FLP) showed that consensus (satisfying above conditions) is impossible in an asynchronous system where any one process may fail • No bound on message delay Set 9: Fault Tolerant Consensus

  5. Circumventing FLP To circumvent FLP, we must relax one of the conditions required above for exact consensus: Examples: • Approximate agreement (instead of exact) • Sometimes algorithm may not terminate in finite time Set 9: Fault Tolerant Consensus

More Related