Consensus Queries

# Consensus Queries

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: r Impossibility Result! Consensus is not possible with faulty communications • One of the most famous results in distributed algorithms • (How do you get anything done with these systems, anyway?) The proof uses the concept of “indistinguishable executions” the consensus card game 2008-01-06 CSE481C wi09 - Robotics Capstone, Lec3: Consensus 26 2008-01-06 CSE481C wi09 - Robotics Capstone, Lec3: Consensus 27 Agreement Algorithms It’s like consensus for real-valued quantities • Processors share real-valued quantities • All processors converge to the same quantity. The papers this week are *hard* • So I will introduce this content with two fun activities… agreement algorithms 2008-01-06 CSE481C wi09 - Robotics Capstone, Lec3: Consensus 29 2008-01-06 CSE481C wi09 - Robotics Capstone, Lec3: Consensus 30 4 Instructions: 10 1. Enter your starting number into your calculator. 30 a. 2. Pick another person and average your two numbers. (Add theirs to yours and divide by two) Don’t round off, keep all the digits. Both people should end up with the same number. calculator agreement (30+10)/2 = 20 (10+30)/2 = 20 b. 3. Repeat 12 times. Try to visit different people. 20 20 20 90 2008-01-06 CSE481C wi09 - Robotics Capstone, Lec3: Consensus 32 The answer is 2008-01-06 CSE481C wi09 - Robotics Capstone, Lec3: Consensus 33 Partial Proof 65 2008-01-06 CSE481C wi09 - Robotics Capstone, Lec3: Consensus 34 Reference 2008-01-06 CSE481C wi09 - Robotics Capstone, Lec3: Consensus 35 Simulation 120 110 Time step 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 100 90 80 70 60 50 40 30 person 1 person 2 person 3 person 4 person 5 person 6 person 7 person 8 30.0 10.0 90.0 110.0 40.0 120.0 80.0 40.0 20.0 20.0 100.0 100.0 80.0 80.0 60.0 60.0 40.0 60.0 60.0 90.0 90.0 70.0 70.0 40.0 50.0 50.0 75.0 75.0 80.0 80.0 55.0 55.0 52.5 62.5 62.5 77.5 77.5 67.5 67.5 52.5 57.5 57.5 70.0 70.0 72.5 72.5 60.0 60.0 58.8 63.8 63.8 71.3 71.3 66.3 66.3 58.8 61.3 61.3 67.5 67.5 68.8 68.8 62.5 62....
View Full Document

## This document was uploaded on 03/02/2014 for the course CS 481 at Rice.

Ask a homework question - tutors are online