Tutorial: Observing Distributed Computations through Lattices

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Tutorial Observing Distributed Computations
through Lattices

• Sule Simsek and Dr. McMillin
• September 24, 2009

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Outline

• Background on Distributed Systems
• Visual Examples
• latGenU Program
• Q A

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Background on Distributed Systems

• Event Global vs. Local
• Order on Events (Happens before relation)
• Sequentially related
• a, b on P a ?s b
• Causally related
• b, c on different P b (send), c (receive), b
  ?c c
• Transitivity
• (a ? b and b ? c) then a ? c
• Concurrent
• If (d ? c) and (c ? d) then c // d

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Background on Distributed Systems

• a, b on same P a ?s b
• b, c on different P b (send), c
  (receive), b ?c c
• (a ? b and b ? c) then a ? c
• If (d ? c) and (c ? d) then c // d

P1 P2 P3
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Background on Distributed Systems

• Vector Time-Stamp a vector of discrete clock
  values one from each p (p, process)
• Global State G ? P( P, Dist. Computation)
  such that (e2?G) ? (e1 ?s e2) ? (e1?G)
• Consistent Global State (Cut) CGS ? P
  such that (e2?G) ? (e1 ?c e2) ? (e1?G)
• Time-Space Diagram modeling P by using partial
  order
• Lattice Representation all possible CGS of P

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Vector Time Stamp (VTs) Algorithm

• Process Pi
• VTi1..N 0, 0, ..,0, N (3 processes)
• Local Events VTiself
• Global Events
• Send Event VTiself
• Piggyback entire VTi
• Receive Event for j1 to N do
• VTj1..N max(VTj, VTi) (component-wise
  maximum)
• VTiself

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Background on Distributed Systems
Time-space diagram P1 P2 P3
P1 (100) VT1self P2 (110) max(100,000)
100 VT2self 110 P3 (001)
VT3self P2 (121) max(110,001) 111
VT2self 121
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Background on Distributed Systems
Time-space diagram P1 P2 P3
Distributive Lattice
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Example from The Textbook
P1 P2 P3
Happens-before DAG Execution DAG
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latGenU Program

• How to Download
• How to Extract
• Screen Snapshots

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latGenU Program (with and example)

Produce a Scenario Lattice Generation Post-proce
ssing
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Produce a Scenario

• Data format

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Lattice Generation

• Gnodes, Consistent Cuts, Concurrent and
  Sequential Paths

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Post-Processing the Lattice

• Before and After Snapshots of a lattice

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Questions??
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Homework

• http//web.umr.edu/ff/classes/384/hw2a-sp06.htm
• Due 2/7/2006